Actually, I'm in the process of opening up a new online store to sell hard-to-find items for PCs and car stereo. I have been in contact with Dension about the possibility of becoming an authorized product reseller. (I own a Rio MP3 Car myself, and it's unquestionably superior to any of these other devices -- but even off eBay, I had to pay over $650 just to get my hands on a new 20GB model. Ouch!)
The reason I think the Dension DMP3 has a lot of promise is the low cost. Everyone seems to know about the Neo MP3 player, but not the Dension. (Even Best Buy is selling the Neo for $399.95 now!) I can't see any differences between the two products, except the Dension doesn't yet offer a USB model - and the Dension comes in considerably cheaper. (Not to mention, they offer it in several case styles, which is a nice touch.)
Also, the Rio fitting in the dash isn't really *quite* all it's cracked up to be. Since it's designed around the now obsolete "pull-out stereo" concept, many newer vehicles really don't provide a good way to mount the cage for it. I had to completely butcher up things in my 1997 Toyota Supra to get my Rio MP3 Car mounted securely -- and I'll have to buy a replacement dash trim piece if I ever pull it back out of the car.
I can see where for most people, it's just as good (or better) to mount the player in the trunk or under a seat, and just affix the remote display someplace convenient.