I do not think that rx550 is not suitable for mining.

Now rx550 gets same 10mh in ETH as rx460 in default settings.
But flashed rx460 with optimized timing and overclocked generates 14mh in ETH.
So I think that if there are a  way of flashing rx550 with optimized timing, it will also gives same 14mh in ETH.

Does anybody have successfully flashed radeon 550?

Yes, I have installed 17.5.2 and gpu-z detect card.
But when I run atiwiflash with admin mode, it says that no still card found, same if I run atiflash -i from command line

Hi,
I've bought sapphire radeon rx 550 4gb pulse.
But atiwinflash  v274 does not detect this card.
Does anybody know how to flash this?