I had a sena, 20S if I remember right. It was on my helmet for about a day.
Biggest complaint was the mount. It clipped onto the bottom of the helmet, extending down about an inch. Caught on my shoulder every time I turned my head, and the helmet sat sideways on a flat surface.
The UI was terribad. The buttons/dials and press/hold this button, tap the device twice, stand on one leg and rotate the dial clockwise, etc made no sense. The app was useless.
Took that off and sold it...
...bought a Cardo. I'm running Freecom 4x's on two of my helmets (dirt and dualsport).
The app is functional. The voice commands work pretty well. IT"S WATERPROOF. Battery life is good (8 hours or so).
Since I got the same kit on two helmets and I won't ever be using both helmets at once, I can take the 2nd unit and swap out on my helmet when its battery dies. On my big bike I can charge it in the side case.
Biggest thing is to get the same make and model~ish that your riding partners use. They have some compatibility modes, but you lose a lot of features (call quality, mesh) using that.
I don't use it for the intercom, just bluetooth to phone for music and radio for radio.