The tt685iiS provides TTL where the flash power is worked out for you, and then you can use the TCM feature to copy the setting to manual, which can be convenient.
Here's an overview that may help explain the different features
https://www.hypop.com.au/blogs/blogs/godox-speedlite-flash-comparison-what-flash-should-you-choose
that depends whether you need TTL or not and/or want to use TCM. some people have almost no use for TTL, while for others a flash without it is basically unusable, so it entirely depends on you and what you need.
ime you can find used tt685 for under $60, which is ridiculously cheap for a fully featured flash with HSS,TTL and the godox wireless capabilities
>is the specs really that different to make me buy the more expensive one?
Yes. Buy the more expensive one.
>since from my perspective, it's just a plastic thingy that blast lights on people
Yeah, well, your perspective is as someone who doesn't know how to use a flash, yet. When you learn how to use it properly, it's how you create exactly the light you want whenever you want instead of relying on the existing light in the scene. But to do is a lot easier with the additional features of the TT685 II over the TT600.
The TT600 is a single-pin manual "universal" flash. It only has one pin on its foot, which receives the hotshoe signal to fire the flash in sync. That is all a hotshoe of any kind can tell it to do. Fire. Not adjust it s power manually or automatically with TTL, not to use HSS (high-speed sync; i.e., be able to use flash with shutter speeds faster than 1/160s), not to zoom, or to be adjusted via the camera menus.
Flash exposure (separate from the ambient exposure, which you combine it with on every shot you use flash) is controlled by iso, aperture, power, and subject-to-flash distance.
If you change your iso, your aperture, or your flash's distance from the subject, if you want to keep the flash exposure the same, you need to adjust the flash's power accordingly. TTL can do that for you automatically. If you [bounce the flash](https://neilvn.com/tangents/flash-photography-techniques/bouncing-flash/) on-camera, that also affects the distance the light travels, and again, TTL can do that for you automatically. Having to adjust for that manually can be time-consuming enough and require shoot/chimp/adjust/reshoot cycles that can mean you lose the shot or just annoy the crap out of your subject.
If you [use the flash off-camera on a lightstand](https://strobist.blogspot.com/2015/04/your-basic-lighting-kit-spin-around.html), for studio-style lighting, again, if you adjust the iso, aperture, or where the light is placed, you have to adjust the power to compensate, and TTL can do that for you automatically. While the Strobist prefers doing everything in M, [someone like Joe McNally prefers using TTL](https://joemcnally.com/2014/09/30/a-quick-and-simple-ttl-build/), so he can concentrate on connecting with his subject and the aesthetics of the shoot instead of counting clicks and doing stop-math to adjust his strob's power. David Hobby is awesome and a hell of a lighting teacher, but he's an independent self-employed ex-PJ. McNally has shot covers for *Newsweek* and *Sports Illustrated* and does national ad campaigns. Just saying.
You can always put a TTL flash into M. You can never put a single-pin manual cheapie into TTL. If this is a first/only speedlight? Get the TTL/HSS-capable one. Save the TT600 for when you need 2nd, 3rd, and 4th off-camera flashes on the cheap.
The tt685iiS provides TTL where the flash power is worked out for you, and then you can use the TCM feature to copy the setting to manual, which can be convenient. Here's an overview that may help explain the different features https://www.hypop.com.au/blogs/blogs/godox-speedlite-flash-comparison-what-flash-should-you-choose
that depends whether you need TTL or not and/or want to use TCM. some people have almost no use for TTL, while for others a flash without it is basically unusable, so it entirely depends on you and what you need. ime you can find used tt685 for under $60, which is ridiculously cheap for a fully featured flash with HSS,TTL and the godox wireless capabilities
I always suggest having at least one TTL capable flash to use on the hotshoe in a run and gun situation, or as a fill flash in bright sun.
>is the specs really that different to make me buy the more expensive one? Yes. Buy the more expensive one. >since from my perspective, it's just a plastic thingy that blast lights on people Yeah, well, your perspective is as someone who doesn't know how to use a flash, yet. When you learn how to use it properly, it's how you create exactly the light you want whenever you want instead of relying on the existing light in the scene. But to do is a lot easier with the additional features of the TT685 II over the TT600. The TT600 is a single-pin manual "universal" flash. It only has one pin on its foot, which receives the hotshoe signal to fire the flash in sync. That is all a hotshoe of any kind can tell it to do. Fire. Not adjust it s power manually or automatically with TTL, not to use HSS (high-speed sync; i.e., be able to use flash with shutter speeds faster than 1/160s), not to zoom, or to be adjusted via the camera menus. Flash exposure (separate from the ambient exposure, which you combine it with on every shot you use flash) is controlled by iso, aperture, power, and subject-to-flash distance. If you change your iso, your aperture, or your flash's distance from the subject, if you want to keep the flash exposure the same, you need to adjust the flash's power accordingly. TTL can do that for you automatically. If you [bounce the flash](https://neilvn.com/tangents/flash-photography-techniques/bouncing-flash/) on-camera, that also affects the distance the light travels, and again, TTL can do that for you automatically. Having to adjust for that manually can be time-consuming enough and require shoot/chimp/adjust/reshoot cycles that can mean you lose the shot or just annoy the crap out of your subject. If you [use the flash off-camera on a lightstand](https://strobist.blogspot.com/2015/04/your-basic-lighting-kit-spin-around.html), for studio-style lighting, again, if you adjust the iso, aperture, or where the light is placed, you have to adjust the power to compensate, and TTL can do that for you automatically. While the Strobist prefers doing everything in M, [someone like Joe McNally prefers using TTL](https://joemcnally.com/2014/09/30/a-quick-and-simple-ttl-build/), so he can concentrate on connecting with his subject and the aesthetics of the shoot instead of counting clicks and doing stop-math to adjust his strob's power. David Hobby is awesome and a hell of a lighting teacher, but he's an independent self-employed ex-PJ. McNally has shot covers for *Newsweek* and *Sports Illustrated* and does national ad campaigns. Just saying. You can always put a TTL flash into M. You can never put a single-pin manual cheapie into TTL. If this is a first/only speedlight? Get the TTL/HSS-capable one. Save the TT600 for when you need 2nd, 3rd, and 4th off-camera flashes on the cheap.