I've tried a few solutions. Ones that worked poorly were the Mpow Bluetooth receiver + wired earbuds, and the cheap Sena-knockoff helmet headsets mentioned previously.
I got nowhere near the advertised battery life with the Mpow receiver. It's supposedly 10 hours, but I didn't get anywhere near that in practice. More like 4 hours, on a good day.
The other problem with the Mpow receiver was that it would report 30% battery remaining, then suddenly shut down. So the battery percentage was either flat out being faked, or being estimated very badly.
That happened with both the original Mpow, and its warranty replacement unit. Either I got 2 defective units in a row, or the advertised battery life is BS. Suspect the latter, given the price point.
I gave the Yideng (or Fodsports or whatever other Chinese-brand-of-the-week) BT-S2 headset an honest shot, but it didn't deliver. Highlights: crummy battery life, no ability to recharge while in use, low volume, zero compatibility with other brands (such as a friend's Sena).
That said, the various Sena-knockoffs do have their place. They're OK if you don't ride at highway speeds, don't go on long rides, and don't need to talk to anyone using a different brand of headset.
The BT-S2 clones could be very useful for motorcycle instruction, especially given the price point. That's assuming one BT-S2 will actually connect to another, which I haven't tested.
Since I didn't care for the popular cheapo choices, you might ask, what did I end up with? Cardo Q-Solo.
It isn't the best, but it's a big improvement on the other devices. Volume is adequate (actually audible through earplugs!), controls are easy to use through gloves, it's waterproof, Bluetooth connection is reliable, and battery life is OK - 5-6 hours. The Q-Solo can be charged while in use, which is hugely useful. It makes the battery life mostly unimportant. All around, it's way better than the cheap alternatives.
Q-Solo retails for around $100 but I got mine for $40 through (long story). No intercom function, but I never ride with anyone so that's fine. Phone calls through it work well, though I rarely do that.
2007 Vee with too many farkles and 50k+ (s)miles