I bought 3 Model Ms on ebay. One labeled as new (got it for $7). I have no reason to believe it was not new. It came pristine in the original box.
I also got an used M and a Space Saver M. They all came in great conditions, working perfectly. These things are so cheap that it's worth to try. If they don't work, you don't loose much.
Go for it. The Model Ms are the benchmark. I tried Alps, Cherry, and all. At the end, I always go back to my old Ms.
And if you want a new Model M, there is a company that still produces them. Search the forum and you will find it.
Good luck.