I hope you dig them. I never tried a 55hz G12M, but love the 55 hz G12H's, and 55hz G12-65's I have. I also have a Pulsonic cone Fane 55hz 25 watt speaker from the late '60s maybe early '70s that sounds awesome. That was paired with a Pulsonic cone Fane Pop 20 in an open back 2x12.
Unfortunately my Hiwatt blew the 20 watter even though I had the cab paired with a 1x15 open back cab to eat half the wattage, and was running it through an attenuator with the volume backed down a pretty good amount. That set up was awesome for '60s/'70s rock clean to mean with the volume knobs on the guitar, then goosed with a Treble Booster to make it get really nasty.
I wish they'd make 55hz 65 and 75 watt Creambacks. I don't trust 25 watt speakers with my Hiwatt, even a quad. Hell, I worry about my 55hz G12H30's I have X patterned with Fane AXA12's in one 4x12 after the above happened.