It's like buying off-brand anything on Amazon.
For example, I had a Prz coupon appear in my newsfeed for Amazon at $7.50 for thermal tights with Chamois and I ordered a L which is what fits me for "on-brand" (Endura, Sugoi, etc). The fit was roomy in the crotch, the material felt cheap and the pad color was a shocking bright green. Did they work? Sure - they were never my first choice in the cold, but they were presentable, relatively warm and didn't fall apart. So when a coupon appeared again for $7.50 tights (not thermal) I ordered an M thinking it would solve the fit problem - but they are far too tight. Again - they're serviceable, but if something else is clean they remain on the bench.
So I've spent $15 on two off-brand tights that would have cost me at least $125 for a name brand. On reflection, I should have just stuck with name brand because every time I wore them I wouldn't feel a pang of regret that I spent perfectly good money on something I don't really like...but in their role back-ups to wear only when others are dirty, they'll stay in the dresser drawer so I've probably lost nothing in the bargain.