I'm really not trying to be a argumentative, but I must be getting the good ones of the batches, of well, everything cheap I guess.
I've not had any issue with the 20 dollar flip up sights, besides them usually leaning to one side, the same side (right) and needing to shim them up.
I don't generally spend a lot of time flipping them up or down, but the rear will go up anytime I'm trying to shoot something small with my red dot.
That isn't to say you won't get a crap set, but my experience has been positive.