Then I found this from MidiPlus:

$39.95 on Ebay. From China. $78.50 on Amazon with same day shipping. Or, you could buy the "Official" version: from MidiTech DE

for $199.00.
First lemme say that MidiPlus products from China are the exact same item as the MidiTech products from "Germany". MidiPlus is the manufacturer. MidiTech products are generally sexy black while the MidiPlus products are some other color like blue or grey or white. So.... at $39.95 vs. $199.00 it's truly apples and apples, except for the anodized color. That's my experience with MidiPlus. Solid quality at a fraction of the cost of the SAME item from MidiTech.
So WTF is it? It's a 128 preset GM module (sounds like 8 or 12 bit with 16bit 48Khz circuit) playing all those mostly cheesy XG and SoundCanvas patches, most of which suck but some of which are very usable for sketching stuff out or just plain practicing without a phone, computer or bulky keyboard. Combined with a small keyboard, like the iRig Prokeys USB 37, you can go anywhere. It's self powered by a rechargeable internal battery, that will power a USB keyboard (or charge your phone - heck, it's as cheap as a standalone phone battery and has a class compliant USB interface AND a straight MIDI DIN connector to a 128 preset 64 voice synthesizer as a bonus). Plug in headphones (or even into your system) and work stuff out.
The thing responds to pitch wheel, MW, pedal, program change, volume, etc so you don't even have to touch it, which BTW is about the size of a deck of cards.
How does it sound? Basically as good (or as bad) as the time-worn SoundBlaster GM stuff that we thought was great way back when. And for what it is, your most basic Bread and Butter sounds are there. Nothing fancy. You'll have to tweak your keyboard's velocity curves to suit and the reverb is global across all patches so you will have to assign a CC to it or adjust the knob on the unit. No other effects from the panel but I'm going to see if GS type stuff is available from CC's over MIDI, like chorus, other reverbs, vibrato, etc. And also see if it responds to splits and layers because the GM spec is multi-timbral across 16 channels. (I'll report back on that after I get around to it).
Clearly, it's not an SF2 GM replacement or HyperSonic GM module, or even a TTS-1 or XG but it does the job in a cigarette pack form factor. Practice or jam or write ANYWHERE without a damn phone or computer. The battery lasts like 5 hours while powering a USB MIDI keyboard and you can use a backup phone battery to recharge it or keep it alive longer. (And you can also charge your phone with it).
Stuff your cheapo light little keyboard and this in a small bag with earbuds and truck and travel anywhere.
I'm not talking about replacing my investment in expensive pro-quality tools and toys here, but at the lower end of the spectrum, this little setup is really neat to have ready at a moment's notice anywhere, anytime. That's not to say I don't expect to see a little DSP or VST thingy this size one day, perhaps soon but surely it will cost big bucks.
For what this little MIDI setup does, I love it. It goes anywhere.