This item caught my on eBay. A big metal box touted by the seller as a "Gameboy Developer Unit (Game Boy) Dev Kit Bundle". Well, after some cursory inspection, I can almost certainly say that this is in no way an officially licensed Nintendo product.
Let's do some cursory inspection of the item from the pictures and text.



As the seller says, "It's all metal so it's heavy but there is no interference from other devices when your playing so the signal quality is superb." We're seeing a solid metal box with a big clonkin' power switch and nice big heatsinks on the sides for superior heat dissipation. (Hey wait a minute...)
The cartridge appears to be an EMS 64M USB cartridge moved to a generic GB game shell. If you look closely you can see how the cartridge case doesn't actually close completely. Look at the full size image on eBay if you're interested. (EMS's own cases are taller on the top part of the cartridge to accommodate the USB mini connector.)
The SNES controller seems to have an extra wire wrapped around the cable. I'll come back to that in a sec.

This is the back panel where a lot of the connections are made. The most interesting shot of the unit, and coincidentally the only one that is blurry.

So what do we have here? Stereo audio out, and the proclaimed S-video and composite out. So far so good. Then there's the DB9 connector that sticks out like a sore thumb. And where does the SNES controller plug in?? And what's that extra wire I remarked on before??? The seller claims "For controls you plug in a generic SNES controller." But I believe this to be false. I believe whoever made this unit modified the SNES controller and was 1 wire short of the number needed for all the buttons in the cable with most wires that he had lying around. This would also explain the DB9 connector, 8 buttons + ground. Note how the images are conspicuously leaving out the other end SNES controller cable.
And I need not add that Nintendo would not release a product with a single wire running on the outside of a cable like that.
So what games does it play?




Pokemon Silver, Super Mario Advance, Super Mario 1, 2, 3, 4, _16, HEY WAIT A MINUTE. The seller does claim "You can also install numerous games at once like pictured.", but these look like a preset list of games that would come with a GBA clone. Yep. This simply appears to be a consolized GBA clone or something of that nature, in a case belonging to maybe an old projector judging from the case.
So who is the seller, exactly? The seller claims "I'm selling my NTSC Gameboy developer kit. I don't know much about this, but it is fun as anything." I did some basic research on this as well. Searching for xcrossxi3 on a certain well-known search engine gives a YouTube channel with an Atari Portable as the only video. Interesting. Let's refine the search to xcrossxi3 site:benheck.com. This leads back to a well-known name around here, SonyPortableizer. His homepage as listed here on the BH forums is http://www.freewebs.com/xcrossxi3" onclick="window.open(this.href);return false;. inb4 all SonyPortableizer's posts that mentioned xcrossxi3 will say "last edited 2013-07-08". In that case, the Google cache will still linger for a few more days.
All of a sudden "I built this and I'm asking for a massive overprice" seems much more likely than the claim "I don't know much about this".
So what appears to have happened SonyPortableizer took a GBA clone that has video out, and put it in a random big-ass metal case. He then sells it with a starting bid of $310 and probably hopes that someone will (nudge nudge wink wink) think it's some ultra-rare development equipment from back in the day and start bidding like crazy. (Granted, nowhere does it claim to be official Nintendo brand development equipment, but that's obiously what he wants you to believe.)
SonyPortableizer, I'm sure you've put some small amount of work into this, but the lies and deception sure leave a bad taste in my mouth. As you're a regular on this forum, you'll sooner or later see this thread. When you do, feel free to comment shattering any and all misconceptions I might have about the issue.