On the plus side, the speaker kind would be completely legal Problem I had when I went that route, is that I still wanted to wear earplugs to keep down the wind noise. Which meant I had to play the music very loud through the helmet speakers to hear it, without going to a powered amp I just couldn't get it loud enough to hear clearly through my earplugs. Maybe with your helmet/windscreen/speaker setup that won't be an issue for you. Worth giving it a try for $20 I suppose

Many long distance riders use the ER6i, thats where I first heard about it actually.