First, there are two variants, the 550-512 and the 550-640. The former is weaker than the latter.
Second, in the US, for the 4GB models, the cheapest, lowest end 550 and cheapest, lowest end 560 are, as counterintuitive as it seems, $120, and $99, respectively. The lowest priced RX 570, a FAR more capable card, is $115.
https://pcpartpicker.com/products/v...92&sort=price&page=1&P=4294967296,51539607552
Unless your friend absolutely NEEDS a card that does not use a PCIe connector, then do NOT get the RX 550.
If your friend is buying new, and buying in the US, go with an RX 570.
The ONLY possible problem with getting a modern-era card like the RX series is if your friend's PC is an OEM one (like Dell, HP, etc) - I know with certain Sandy Bridge (all the i3-, i5-, i7- chips with numbers ending in 2xxx) Dells, they simply would NOT work with RX card (and some R9 cards).
If, on the other hand, this was a system put together with his own purchased motherboard, etc., then it should probably work fine.