Some data points: I bought a Decathlon folding bike (Fold 500; new, ~450€) a few months ago. Using it many times a week (probably more than it's intended).

No issues so far. Internet reviews (https://www.decathlon.fr/r/velo-pliant-fold-500/343354/undef...) are quite positive as well.

I've had other Decathlon bikes when I was a kid/teen, I don't recall any issue either.

N=2, but my Decathlon bikes have well over 50000 km between them with no issues, beyond the usual wear and tear. Value wise, they are fantastic. They are road bikes, however, not the folding specifically.

This is what a lot of people want to be true, but in fact is not. I believe it can be mostly explained by the "IKEA effect": any given model is bought by so many people that the inevitable design defects are quickly found and remedied.

Of course you get what you pay for. Note that this is not Decathlon’s cheapest folding bike.

Skill issue/maintenance issue.

i have (had) several cheap (under €500) single speed bikes and Decathlon is not the worst of them