A few quick points:
I never intended to make a direct comparison to Sena, or any other top end unit when starting this thread. I only wanted this unit to have my google maps girl piped into my ears so I wouldn't need to take my eyes off the road as often when touring. For this purpose,for me, I honestly could not be happier after 3 long weekend trips 2 up. Anything in addition to that is truly a bonus for me. I still haven't given the battery a good test, for I take my chargers on the road with me, and after using it for the weekend, I charge it up again the night before I am heading home. Considering it only takes an hour, 1.5 at the most to charge, it probably has a lot of battery left before I charge it. I don't think it is fair to compare this unit to something at least three times the price. But, considering that is what always ends up happening, it's shortcomings to value ratio comes out pretty well ahead in my opinion.
The connector definitely seems to be a proprietary piece. It's obviously not a micro usb, and it doesn't match the much less popular mini usb I have that came with some old chinese tablet I once had. I do think I have seen this connector somewhere before,I just can't remember where. It's possible it was a little infra red rc helicopter I had a while back I used to play with my dogs and cat.
Andrew, all I can tell you is I can not use mine at full volume when listening to music because I fear hearing loss. I assume helmet design has a lot to do with it, and as I told you, I know placement makes a huge difference. The one piece of advice I can give you is, after finding the sweet spot for mine, they seemed like they would be too far forward when looking where they are placed in my helmet. My helmet has to holes about a 1/4" in diameter that I assume I could route wires through. I would also assume that are centered for where speakers would be mounted. However, mine are mounted about 3/4" forward of center of those holes.
I think having 2 makes a lot of sense for a few reasons. Extended battery, back-up propriety cable and speaker/mic.....etc. You might even meet that special someone you adore so much you don't mind having her piped directly in when riding. Long shot I admit, but it could happen !!