Argthtjtr

I did some research regarding off-brand flashes and I think TT600 (I would order 3 of those) would fit me perfect for my needs. I would use it mostly for product/advertisement photography with light stands/softboxes/umbrellas, and also for portraits. I use bunch of different brand gear (mostly Canon, but also Sony, Nikon and Fujifilm), I don't mind it doesn't have TTL, it supports HSS with corresponding trigger (I would go for Godox XPro Canon version), it has built in RF receiver and it's output power can be controlled via transmitter, it's not brand specific so it can be mounted on any hotshoe if I would use it on camera. And also it's pretty cheap (56£).

Other option would be Yongnuo 560-III which does it all except it doesn't support HSS if I'm not wrong.

I want to know if I'm missing something or if there is some other-brand flash that would suit my needs better within same price range?

In that price range? No. But in terms of camera gear prices (like say, a new lens), it's not that much more expensive to move up to the TT685.

And the main disadvantages to going with the YN-560III/IV/-660/720Li models are not only that they don't do HSS, but also that the system doesn't have expansion options past speedlights, and that the Yongnuo TTL gear doesn't work in concert with the manual-only gear or the RT clone gear, so you can't just add TTL/HSS gear into the mix later.

The Godox TT600 will work with the larger lights in the Godox line, and interoperate with Godox's TTL lights.

What you have missed, however, is that you'll only get HSS from your Canon cameras if you're using the XPro-C. To get HSS, the transmitter has to match the camera hotshoe to receive the HSS signals from the camera. The pins on the foot and the electronic communication protocol are different in all the systems (particularly Sony's whacky multi-interface shoe), so to get HSS from your little TT600 from all four systems, you'll have to have an XPro-C, X-ProN, XPro-F, and XPro-S.

Secondly, the TT600 is not firmware upgradeable. You cannot take advantage of any new features added through firmware upgrades. So, unlike having a TT685C, you will not be able to use ID codes, and you won't be able to turn off that freaking annoying blinking LED on the front that indicates the flash is in radio slave mode.

Thirdly, the trigger built into the TT600 is not a receiver. It's a transceiver. You can actually use a TT600 on-camera as a transmitter, but because it only has the single pin, it can't receive any communication from the camera except the sync (fire) signal, so it cannot be a TTL or HSS master. You will get remote power control.

Fourthly, trying to use a single-pin flash for on-camera event shooting can be a serious PITA and cause you to miss shots, as you dink about with power settings because you had to change your position or follow someone into different lighting, or you have to bounce for that spot over there and guide number calculations only work for direct flash. Event shooting (or kids) typically don't let you shoot, chimp, adjust and reshoot. Timing is everything with events. So, TTL, imho is certainly worth it in at least the one speedlight you use on-camera, as well as your off-camera key light. Because TTL (if your triggers can do TTL locking, which the Godox XPro can) will let you drag the iso and aperture as well as the shutter speed, and can really speed up setting up your key light if you tend to have a dynamic workflow where you like to play with light placement and iso/aperture settings and move fluidly between setups.

Not wanting to pay for TTL is not the same as not needing/wanting it. :D Particularly if you've never used it. Like full frame, you may not need it, but there are certainly reasons to prefer it if you can afford it. Just as there are reasons to use aperture priority instead of full manual and vice versa.

Just me, but pick which camera you're most liable to use the flash on the hotshoe with, and up the budget to get a TT685 for that one system. If you have all the XPro triggers, it'll become a TTL/HSS slave to them, if the firmware's up to date. I use a TT685-C in TTL/HSS/remote power control from an XPro-C on a 5DmkII, an XPro-F on an X100T, and an Xpro-O on my Panasonic GX7. I chose the TT685-C because it also does Canon "smart" optical slave/master, and I have a 580EXII, so I've also got a backup triggering system if radio interference is causing issues. Only the Godox -C/-N/-S versions of the TT685/V860II do this, btw.

I also own two TT600s, and I'll grab the TT685C first every time for off-camera. Because I don't have to remember that the XPro-F isn't doing HSS with a TT600 right now. :)