I have tried the SM mousse, and I have also tried the Deva mousse! Although my hair is not fine, it occasionally seems to get weighed down, thus my mousse purchases.
I bought the SM mousse first, and I have to say that although I love absolutely everything else in their line (esp their new cowash), I wasn't a huge fan of the mousse. That is to say, I didn't dislike it, but I was just kind of neutral. It seems to be conditioning and non-greasy, which is great, but it doesn't seem to DO anything to my hair, if that makes sense. I was slightly crunchy after using it, and that's the only effect I could discern.
The Deva mousse, on the other hand, has definite effects. It holds my hair in position almost as well as a gel and it seems to be curl-enhancing (although I don't know if that was the mousse or just a good dew day, lol). Thus far i have definitely preferred it to the SM.
Having said this, I've only given the SM two tries, so I'll update if I try it again! I've seen a couple other reviews floating around; hopefully those folks and others will chime in!