Don't have a Glock so don't have experience with that specific holster. But I do have Serpas. There was a problem with the locking mechanism getting bound up if anything got behind the innards. They fixed that so it is much harder for that to happen.
Being as how they will always build a better fool, nothing is foolproof. However, I'm not worried about my new-gen Serpa failing me. Thousands of others seem to feel the same way, and there are no reports of the new-gen ones failing like the old one did.