Got a large Space Case over 20 years ago and never looked back. There was a vendor that was giving away small 2 piece Space Case grinders a while back without me knowing. Had several purchases of just papers and was surprised to find a grinder in the package too. Kept one gave the rest away. Seemed like a losing deal on the vendor's side.
A friend got a Kannastor a while back. Good grinder until he had the smart idea to clean it in the dishwasher. Thing corroded over and that was that.
Nothing wrong with factory seconds. The polished aluminum is going to get scratched the moment you take it out of the box anyway. Seems like a good deal.
Bottom line, grinding cannabis is a simple thing that doesn't require a NASA designed, or priced, unit to achieve the desired results. I've seen old grinders with missing teeth that still do the job and the results taste the same. If you have the means and want to pay up go for it, otherwise try to not overthink it. I do share your concern about plastic grinders shedding during a grind and would personally look for aluminum, but I also wouldn't turn away someone who wanted to share a bowl with me filled with weed they just ground up in their plastic grinder.