They are popular to a certain degree. I've been known to sport an Ampeg BA110 on some of my gigs...just used it on my gig today with a PITA load-in. And it was not only my floor monitor but I used it for the entire room. Wasn't a big room and we're not crazy loud or anything, so for that particular gig under that set of circumstances, it's perfect.
Only problem with little floor monitor amps I have is the lack of a big sound. I just don't find them as inspiring tonally. I've never played a small cab that didn't sound greatly improved by the addition of a second matching cab. Even one of these super duper high power little combos don't get it done for me because they're small. So for that reason, I usually at least bring a medium rig like a 215 or a 410, and that's only because I don't always feel like bringing an 810. I'll be the first to admit that bringing small stuff is a tonal compromise for me, but try boarding a casino boat and riding up to the 4th floor in an elevator with an electric bass, an upright bass, and an SVT