The rx8 is way above the MMM IMO. I had 2 MMM and 3 rx8 already and here are the results:
MMM:
- closed case, if the fan dies -it will- you have to open your ESC
- the case is closed with plastic clips -> FAIL, they are weak
- if you want your MMM to be strongly attached to your car it needs a minimum of 2 zip ties, with the RX8 I just use velcro
- the switch has to be removed too, it's very bad built
- it's heavier, sits higher too
- to set it up you have to open your receiver, use a castle field etc etc..
- sensorless only
- 150A
RX8:
- better quality overall
- case closed with screws
- fan can be removed without opening anything, in most case it isn't even needed
- you set your car directly with the mode and set button
- smoother feeling
- sensored and sensorless
- the only thing that is hard on this ESC is the soldering, you will need a solder station that gets hot fast and don't wanna stay to long soldering your cable BUT efficient wise it's better having NO connectors
- 200A
- nicer looking
- software is really complete, more tuning options compared to the MMM
-....
I fried both a MMM and a RX8. The first one because the case opened and the second because I might have damaged a component while soldering the cables for a too long time. So in each case I could have avoid it.
I didn't tested the Xerun but the feedbacks are excellent for the price. This is the best option to save some bucks