there are reasons why they are cheap, one of it they can be rejects from branded factory so they get them for free or below cost as scraps

maybe you can have issues, maybe you won't
I've used a RM60 fork with very good results, but ymmv

a few things you're not doing right, try search the net for guides and tools you need:

- that's not how you open a fork tube
- if you can't open a fork tube, then you cannot inspect the most important component in the fork which is the damping rod
- cheap doesn't mean bad, I would take a closer look between Apido vs Faito 15wt differently - thickness, lubricity, foaming characteristics, etc
- I'm using 25wt Motul fork oil in my RM60 forks (yes, the oil is about the same price as the forks)
- 50ml is definitely not enough, I don't measure fork oil by volume, but by depth level... see the back of Apido bottle, it carries some information you can use