I like the Mopho so much. First, and most important. I am a guitar player by practice. I can not really play piano with both hands very well. Guitar, forever brutalized my other hand, making it impossible now to ever truly play anything but simple things with it.
The mopho is a little more than two octaves, beginning on F. But, there is something Mopho can do that Moog little phatty could not. It can be transposed to any key in the major scale, to any mode, to any thing western. Little phatty does have alternative tunings, but I don't use them anyway. This is hugely useful if you play with guitars in a band, and also if you are not a brilliant piano player. You can simply transpose and tune the keyboard anywhere you want to any key.
It doesn't have alternate scales, but I don't miss it. But, the keyboard is brilliant if you want to those old time jazz, rock, fusion sounds. It is very fast, and very good. People didn't like the name. Ok, it is silly. But the keyboard itself is brilliant.
Now with a tetra. You can extend it to 5 voices. It is a Prophet-5 really. Then, you can make all those rock organ sounds, like Deep Purple. It can make brilliant organ sounds of any kind you imagine. I always wanted to be able to play Hammond Organ. But my other hand, is a slab of meat from guitar. It's very hard to pick it up if you first played guitar.
That is just my take on a very brilliant instrument. It can be programmed so many diverse sounds. Imitating hammond organs. It can do all those fat squawky funky bass sounds. It is the most programmable synthesizer of its' kind with 4 LFOs, plus 4 patch bays. Quite a diverse instrument, not just some stupid techno machine.
Now, I wanted an instrument. Something real, to play. Not some stupid controller and software. The Little Phatty though, is very easy to get all those classic rock and fusion and jazz sounds out of it. It is the only moog I will ever need, it does it all. Not sure what a voyager does. But the Mopho can sound also great. The filter is very good. It sounds real. Not like digital stuff. Digital filters never sound right. It doesn't sound like that moog filter. Which is the thickest sound ever. But still, it is punchy and tight.