While it's always good to see someone step up to the plate on this issue I have personally been disappointed too many times with aftermarket polymer mags in the past. Most issues were with follower tilt, or faulty injection molded points causing multiple feeding issues with the weapons system. Honestly, I think that they will work fine for the range and for plinking. As for dropping a full one onto the concrete from chest heights not so sure. If you are really short buy a couple and use them for practice and wait for the OEM FN magazines to become available again at a "normal" price.
I have about 5 Thermolds. Though they aren't as resilient as say a PMag or the factory FN mag, they are fine for range use. Some may think that's crazy, why have separate range mags and 'go' mags. I bought them during the height of the panic when FN mags were scarce. I stocked up on factory mags recently and now these are more or less just there as extras. They feed fine, fit fine. I bought my five @ 22-23 a piece from Brownells back in Feb.
I bought a couple of the Thermolds for $23 a mag. They not the best quality, but certainly good enough for using at the range, like Sarge said. I like using them when at the range so I am not wearing out my factory mags. I got mine from Classic Firearms. They're the same ones you posted a link to just ten dollars cheaper. See link.