Usually, the psyche of people is used to seeing reflexes in the eyes of a round shape - the Sun. Therefore, round ones are more attractive. But you should choose according to the functionality, and not according to the shape of the lamp.

There’s no difference between round and rectangle flash heads other than some of the round heads have magnets in them making it easy to attach compatible accessories. This will depend on manufacturer of course.

Unless you’re shooting straight on a wall in an otherwise dark room, you’ll never notice the difference. You should literally ignore it for the purposes of purchasing. Pick the flash with the features and cost that make sense.

Do you mean the actually head , because for 50 plus years they are usually round or are you talking the soft boxes surrounding the strobes …

Neither. Different applications with different pros and cons.

Anyone telling you a round head has higher ‘quality’ or softer light is at least kind enough to out themselves as an idiot, though. So there is one point for round heads.

Here is a decent write up on comparing them;

I like the quality of light from round flash heads better, but it’s a minute difference besides the reflection. When using diffusers you won’t be able to tell a difference if done right. Don’t get into your head to much about it, especially when you’re a beginner and just go with what your budget tells you.

It makes virtually no difference. The difference in surface area is minimal, so it won’t be noticeably softer and the catch lights in eyes won’t look any different at any normal viewing size.

Such a small difference between the two on camera should not be a deciding factor.

Flashes are fickle things so make sure you get one with a good manufacturers warranty, I buy the flashpoint units instead of the identical godox units just to get the warranty from flashpoint.

A round flash head produces a light patter like this: ( )

A rectangular flash head produces a flash pattern like this: [ ]

Both are fine and are only noticeable is your subject is very close to a background and even then not much.

Personally I prefer round in studio and standard for editorial stuff because the flash can “zoom” or create a narrower beam of light.

If I buy the round adapter is that the same thing or do I still need a round head flash ?

No. Is not better it’s the same.

If you’re comparing the godox v1 to the godox V860iii, in my experience and from the reviews, the v1 is much more durable than the v860iii. Don’t know what’s the issue with the v860 but they have a nasty habit of dying in a year to year and a half.

I have both and the light is basically the same unless you’re shooting a specific shot against a wall. The V1 does have a really handy magnetic attachment mechanism that lets you put gels and a diffuser on it super easily which is actually the main advantage.

The only reason I bought a round head for one of my Ad200pro strobes was for it to fit specific modifiers for a certain look I was going for. But honestly, most modifiers don’t need a round head to work. And once you modify your light, the shape of your catchlight is determined by your softbox, umbrella etc.

round flash heads give a more pleasing catch light in the subject’s eyes, while both shapes can look harsh without proper diffusion.

Not particularly - but there are a number of attachments designed specifically for round-headed flashes that can improve your shot.