HSU claims 32Hz response for the STF-1 and reviewers have measured output at 106dB while Outlaw claims 28Hz response for the LFM-2 at 110dB.

Also, the LFM-2 has a slightly different cabinet design from the STF-1 as well (downward firing ports in the LFM series).

Not overly dramatic differences to be sure, but they are definitely different subs with differnt build and performance characteristics.
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Outlaw 976, Outlaw 7700, Pro-Ject Phono Box S
Sonus Faber Domus Grand Piano (F&C), Niles HDFX (Surr. & Rear Surr.), Outlaw LFM-1 Plus, Velodyne SMS-1
Sonos multi room audio
Video: Sony KDL-46V2500, OPPO BDP-103, TiVo Premiere XL4
2-channel: Outlaw RR2150, SF Concerto Home, Outlaw LFM-2