It depends on the exact model you get, but they can be very good, $50 is a good price point to ensure quality but that one in particular looks questionable, it's best to do your research. For $50 anything you get should at least be able to play up to playstation 1 at full speed, especially if it's a console that plugs into your TV.
>>5974R36S (aka r35s+) is the latest hot handheld chink console, goes on sale for as low as $35 and can play PSX at full speed with several hours of battery life. Has 16,000 preloaded game files but since the SD cards are low quality it's recommended to replace them.
As a rule, don't get anything that only plays NES, because those are scams, anything worth buying will at least support SNES and GBA games even if the performance isn't that great for them.
Best Low-End handhelds:
Data Frog SF2000, Powkiddy v90
Best Mid-tier handhelds:
Miyoo Mini, Anbernic rg35xx, R36S/R35S
I don't know anything about the higher tier stuff, I think at that point most of them are just android devices.