Well, speak of the devil - it came in today.
Go go prompt shipping - ordered on Friday, came in Monday. Of course, I only live a state away from their HQ, so...
Anyway, let's test this thing:
1) Does the plug fit?
Yes. It fits perfectly into the miniUSB slot as expected. It's flush with the bottom of the phone, so the whole device continues to lay flat. Fits somewhat tightly, too (definitely won't just fall out on its own at least).
2) Does it allow syncing, charging, and other standard features via the Mogul to PC USB cable?
Yes.
3) Does it take standard 3.5mm headsets and plays stereo music without problems?
Yes.
4) Can I Sync at the same time I use headphones (and play music)?
Yes.
5) Do you still have access to the stylus while it's on?
Yes. Yeah, you lose access to the microSD slot with it on, but honestly - how often will you be pulling it out? However, it does block the reset hole (as well as everything else that's down there), so keep that in mind.
6) How does it sound? Well, with a decent headset, it definitely won't replace my MP3 player (SanDisk e200 line), but it's more than acceptable. Far better than the internal speaker can put out, as well as what comes with the device.
7) How loud can it get? Well, let's put it this way - my headphones are at about 50%, and PocketMusic is at 42%, and it's plenty loud. I can also jack it up without any distortion issues.
8 ) How big is it on the Mogul? It's about a credit card thick higher than the top of the Mogul, and pretty much the same size on the bottom. Lengthwise, it's just a bit longer (inch or so) than the flay 'bay' on the bottom of the phone. Also, it doesn't add any noticeable weight on the device.
One issue I've already noticed though - if you hold your phone vertically by your left hand, you'll find some serious issues with holding your device once you plug in any cables, as the cables all come out on the left side. However, with a bit of thinking you can get around it. It'll just take a little bit to get used to.
Overall, it's a steal at $5. Get it if you want to use your device for a MP3 player.