This is a common question, and for good reason. Much like speaker preferences often come down to personal taste, I see bass extension as a personal choice.

What I've liked about my LFM-1 as much as the way it can provide strong low-frequency punch on movies is the way that it blends in with my main speakers for music - the LFM-1 contributes to the music, but doesn't advertise its presence. I've heard subs that don't achieve this with music. (Think something along the lines of: "Hey, look at me - I'm a subwoofer! I like this song, but I'd rather have an action movie right now. Bump! Bump! Bump!"). Any sub requires some calibration to integrate with your other speakers, but that goes without saying...

Part of the is also room acoustics. My SVS 25-31PCi was pretty boomy with music in our old house (to the point that I had the mains crossed over at 40Hz so that the sub didn't get asked to do much with music). That boominess stil existed in our current house, but it wasn't as severe. I didn't get the LFM-1 until after we moved, but it integrated smoothly from the get-go. My SMS-1 did refine the sound (most noticeably on movies, where the sub gets more work to do), but since my room acoustics were in decent shape to begin with it isn't as significant as it could have been in a different space.