The "M" denotes the convertible spa - that is the Model designation. It will run on 110 or 220 with a simple conversion. The Tiger River Bengal with the model designation "MM" is the 220-only model. MM spas have a larger jet pump so you can run more jets at the same time. Not more jets, not more power from the jets. Just more jets at the same time. The plumbing is different to allow for this.
They are both considered "EE" series tubs. That means Energy Efficient. That denotes the smaller jet pumps (in this case only one jet pump) and the larger, 5000 watt heater. Some of the other models have the "HP" designation - monster jet pumps and a 4000 watt heater. The HP tubs also have the Tri-X filters in the HotSpring models. Not needed in TR because they are bypass filtration tubs.
Also - the MM model tub comes with the "Amur" waterfall feature - and a two-speed jet pump.
Here is the info from the web site:
Control System
Convertible IQ 2020; 115v/20 amp, (includes G.F.C.I. protected power cord. Or 230v/50 amp, 60Hz)**
Heater
Convertible- No-Fault(R) (1500w/115v or 6000w/230v)
Jet Pump
Convertible Wavemaster(R) 7000
(1.65 HP Continuous Duty,
3.5 HP Breakdown Torque)
Control System
Dedicated IQ 2020; 230v/50 amp, 60Hz, (includes G.F.C.I. protected subpanel)
Heater
Dedicated- No-Fault(R) (6000w/230v)
Jet Pump
Dedicated Wavemaster(R) 9200
(Two Speed, 2.5HP Continuous Duty
4.8 HP Breakdown Torque)
Water Feature Amur(R) (backlit with blue LED lighting)
