The M9 that CDNN is selling is an "old" design. I believe Steyr stopped production of it several years ago. So, the ones being sold now are the "do-do bird", in a manner of speaking. No more will be born.
The reason it is so cheap was due to importation issues - basically, the importer and Steyr discontinued their relationship, and the existing stock was bought out at outrageously low prices - much of it by CDNN.
Expect that if you buy one, it will be at least 3 years old already.
This is NOT a bad thing, and the M9 is NOT a bad gun! In fact, it is an EXCELLENT firearm at an amazing price. MSRP is roughly equal to that of any Glock. The build quality and tolerances of the Steyr are way ahead of Glock.
As far as parts go, magazines shouldn't be too much of a problem. I have seen many internet retailers that stock them, including CDNN. For replacement parts - some people are definitely having a probelm right now. It seems Steyr is reorganizing their US business, and there currently is no importer for parts. As of now, if your pistol breaks, you'll need some luck to get it fixed.
I can say that these ARE indeed very reliable pistols. Personally, I have no reservations about owning and recommending them, even though parts may be hard to come by for a while. Yes, there have been some failures. Some pistols have broken parts. It happens. But overall, reliability is very high.
My personal thought is that for the price, it's worth the "risk". You'll be getting an incredible firearm for an incredible value. *If* something goes wrong, at least you didn't pay out the nose for the gun in the first place.
The new M9A1 is the replacement pistol for the M9. Basically, the polymer has been redesigned and the manual safety has been removed. Other than that, all mechanical parts are the same; even the slides can be swapped between an M9 and M9A1.
The new M:
I can understand the lack of support & enthusiasm for Steyr right now; who wants to buy a pistol with no warranty support and possible lack of replacement parts? Well, at the cheap price from CDNN, I would. I would NOT buy an A1, because the price is in the $450-$500 range. Knowing what I do about my M9 (and S9), I might. But if I were new to Steyr, I'd choose the cheaper "old" M9 over the more expensive redesign, at least until warranty support & parts become readily available again.
Bottom line? Buy it. It's a great gun, and you'll enjoy it. Once they are all gone (remember, they're not being made anymore), the price *might* increase on the used market. For now, you can rest assured that you're buying a fine gun at a bargain price.
BTW - I bought mine partially for looks, also. Next to 99% of the polymer guns out there, the Steyr M is one sexy-looking beast. Some people think it's ugly, but usually they find Glocks attractive - yikes.