I agree totally with the above. You have to try both Bluetooth devices together to be sure they will pair. Some helmet manufacturers qualify what 3rd party devices are known to work - but software and new products are continually changing. Even then I found some issues with my old setup:
I am still using an HP iPaq running Windows CE and TomTom maps. I drop it in my top pocket along with a BT GPS receiver and plug in my earbud. On batteries I can get about 7-8 hours for the combo.
I took it along to my biker shop to try out the BT helmets. I managed to get them paired then spotted (or heard) a BIG problem. Audio sent over BT is pretty demanding on the processor. What I found was when the short navigation instruction was transmitted, the first part was missed. I repeated the test using a short MP3 audio file and got the same result. My conclusion was the BT audio needed to sync itself and this took a short time. Useless for satnav if you miss those first 2 words! Newer BT units may now work better.
I then moved away from BT apart from linking the GPS receiver, because of the battery power. If you want BT freedom on the helmet, you need spare batteries/bike/and mains charger and the mentality to keep everything charged. I have now gone back to a helmet wire and plug, but I'll review a remote setup if battery drain gets better. Unfortunately BT is the worst for power drain and a simple f.m wireless link from bike to helmet would be better and would run for many hours off a small battery. BT options for helmets can be quite expensive and your choice of helmets can be limited. Now I always check a helmet to see if it has side pockets for mini speakers. Some Sport helmets have very little space to fit small speakers.
I have always been keen on audio only, not wanting the distraction of a screen in front of me. BUT the one thing which seems missing from all the new satnavs is a low level repeated audio 'beep' which lets you know the earbud link is o.k and the battery has not gone flat. There is no background noise clue to hear. They could easily do that to prove the GPS is still linked. At the moment, I hold my breath for the first instruction and if that is o.k I'm confident of the rest.
Another curious thing on the legals, is some countries ban the use of GPS speed camera location. As far as I know that comes under their vehicle regulations for anything fitted, but does not apply to what a rider wears or is not physically tethered or powered from the bike.
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