Are they of the ‘square tooth’ belt design?
My 3d printer had a ‘square tooth’ profile belt and it gave issues with inaccuracy. I have since upgraded to 16tooth gt2 pullies and belt and my prints are much cleaner and consistent in general and it instantly fixed the issue I had been chasing for weeks. Your belt might be a better/different design, and you may not have any issues (plus if they were really cheap) I say, give them a go. Just keep this in mind if you have accuracy issues (more specifically repeartability issues)
Just wanted to give a heads up as I spent a lot of time printing upgraded tensioners, changing linear bearings, tightening/loosening assemblies (generally pulling my hair out) chasing a solution to the issue I had, and in the end it was the belt that was the culprit.
Round tooth profile belts are always the preferred option for precision.