oh well if the eBay seller has 4-5 stars then they must rigorously test the ballistic protection offered by a bit of stamped metal and some extruded plastic that cost them LESS THAN £3. Come on now, what level of testing are you going to be able to do? shoot at them a few times with a 3-400 FPS AEG? Then what, so the one you shot up took it, but what about the other 2 pairs. The only way to test something like that is to destruction, at which point you need to know that every pair has been manufactured to the same standards and with the same level of quality control.
If you're seriously considering trusting your eyesight to a £3 set of glasses from china then you'd best get used to dogs as eventually you're gonna need one to do your seeing for you.