I have the Smith kit in a Gyro helmet, fit just fine. I think between the two, the difference in speaker size is minimal that they are almost interchangeable.
As you note, I do seem to recall the controls are different between the two which is why I think I went with the Smith over the tune-up. Then again, it has been two years so my memory may be off.
Listening to tunes in your helmet via these kits isn't like having an earbud jammed into your ear. As long as you don't turn the volume up to 11, you can hear around you (your board, other skier/snowboarders) and have convos just fine while still getting your music as... almost background music.