Basics
This specific pistol can be had from stores such as WGC, Redwolf, and EhobbyAsia. I do not know of any stores outside of Hong Kong carrying these. I ordered mine from EhobbyAsia, with a spare magazine and Marui Desert Eagle scope rings for $221 (total) on Thursday, October 1st. It arrived today (October 5th) through UPS.
Upon tearing off the UPS packaging, this is the box that one is greeted with.
After opening the box, you'll be greeted with the basics. Your Desert Eagle, Magazine, BB's (presumably .23 or .25), cleaning rod, manual, the "Do's and Don'ts List", and several paper targets. Manual and Do's/Don'ts list are in moonspeak. There was no Marui Lineup catalog included, which disappoints me for some reason.
While removing the Desert Eagle from the box, two things become quite evident.
1: This gun is BIG. Having owned an original Marui Desert Eagle, I knew how hefty and large these are, and this is basically the same thing with just a few extra inches of barrel, making the gun just slightly over 14.5" long.
2: The Marui Desert Eagle is built to last. While the externals are primarily plastic, a metal skeleton lines the insides. The metal skeleton ensures that the slide will take a beating, and just adds to how solid the gun really feels.

14.5" of [s].50 Action Express[/s] 6mm Delivering, Gas Blowback Glory.

16" Long with the slide locked back.

The gun is made with complete trademarks, but yours may not arrive unmolested, and the trademarks may be burned or scratched out from customs. This is a gamble you take with any Tokyo Marui product.

The beloved I.M.I. trademarks. The grip on this model is not the same as the standard TM Desert Eagle, however, and will lack the I.M.I. logo.
Hopup
The hopup is located by pulling back a small piece just above the breach. The hopup can be finely tuned, and will deliver some very nice performance.

With the piece forward, the hopup is hidden.

But pull it back, and you are greeted with a very effective hopup system.

Despite the long outer barrel, the inner barrel is standard Desert Eagle length, and does not extend to the end.
Performance
Anyone who has operated a TM Desert Eagle can tell you that these puppies are very fun to shoot. On Green Gas or Propane, a TM Desert Eagle can reach roughly 320 FPS, weather according. I am playing on the safe side, and running Duster through mine, which puts it to about 250-280 depending on the weather.
The hopup provides very nice adjustment, and will deliver some nice performance with the use of .2's up to .3's, all performing well with proper adjustment, and delivering excellent range. I've found .3's to work best for me, offering the most range and accuracy, at the expense of FPS.
Accessories
If you would like to customize your own TM Desert Eagle (10" or Standard), you aren't left with a huge amount of options. Metal slides, body kits, and internal parts are around though, and just require a little bit of searching. TM brand scope rings can be had for the Desert Eagle, and there are some pistol scopes out there that look quite nice. I personally bought the TM scope rings, though they're a bit low, and I don't think any scope can honestly fit on with these rings.

Pistol, spare magazine, and scope rings.
To holster such a weapon, you're going to need something along the lines of a Tornado Holster, or any Desert Eagle specific holster. Some other holsters may work, with or without modding.
Why?
Why choose the 10" over the Standard? In all honesty, there really is no reason. In fact, the 10" is just a longer version, with the same inner barrel. I personally like the longer one more, and a VSR style barrel can fit in if you're able to cut it.
All in all, I'm very happy with my purchase. In the end, it is just the same as a TM Desert Eagle, so upgrading it should pose no problem to anyone with experience.
For anyone hoping to pick one of these up, or even just a standard Desert Eagle, I hope this helps out a bit. Feel free to ask questions, I'll be more than willing to answer them.