They have higher fail rates than originals, originals don't really fail while 3rd party ones have allot of reports.
That being said odds are stacked in your favor and in more cases than not they will work perfectly fine and they often have more storage than originals.
So far in 30 years i only had 2 memory cards fail on me, one was a Blaze 2x for the PS1, that had that little switch for the two memory banks, one of them died just 3 months in and the other was in fact a official Sony PS2 memory card that after some time had read and write errors.
The one that amazes me the most is the Gamester N64 Memory Pak with the 2 dip switches and 4 memory banks, altogether squeezed in the same size and nearly the same weight as a official pak. 25 years and running perfectly fine.
Now if we wanna talk about bad Third party products, i got the Mad Catz Dream Wheel...
Seriously, i think steering wheels are the biggest example of "you get what you pay for", pay cheap and they suck, you have to spend hundreds of euro for a decent one. I got a Thrustmaster TMX Pro for my PC and while that is pretty low tier compared to the serious Sim Wheels from Fanatec (1000+ €) it's light years ahead of all the crappy third party wheels i got for my consoles.