I know this isn't quite what you're asking, but I figured I'd offer my experience for your consideration: I have the Nolan N104 helmet (handsome, modular, light, and quiet, with a flip-down sun visor--10/10!) and Nolan has special "N-COM" bluetooth systems designed to integrate seamlessly into their helmets, which have recesses and removable inserts that make room for the speakers, wires, battery, control panel, mic, and charge port. The controls are small and easy to use even with thickly gloved hands, the mic boom is unobtrusive, and the sound quality is still great after 3 years. And since it's designed around the helmet, it just looks much much better than any of the hulking attachments folks are talking about above.
I'll be replacing my helmet soon, and I'm definitely going with the N105, which is the newer version of this one. I will also definitely be buying the N-COM setup to go with it! The helmet is $440--and it's IMHO the best mid-high range modular helmet on the market even without the bluetooth installed--and the N-COM system is an additional $120 or so. Steep by some standards, but my helmet is a place where I'm comfortable spending higher for quality, features, and fatigue reduction. You use it every time you ride.
So, that's the long explanation behind my short suggestion: If it's not way too soon to replace your helmet or you're open to buying another, consider a Nolan for your bluetooth needs!