Sometimes I do that.
Crank the 101 RESONANCE and patch the CARRIER OUT to CUTOFF. If you use a delay/reverb etc. you can acheive some really cool theremin-like sounds by playing with the CUTOFF knob.
Dunno about using them as a synth; maybe a tuned oscilator ala squarewave?
Hiya - you are the same JSRockit as on the Elektron forum, I hope? 
Yep…I am…and I’m asking the same question…lol. What’s up Jyoti?
I’m just getting a bit obsessed with the Foogers. The Ring Mod looks well tasty, especially since I’ve seen that Squarewave thingy about using it as an extra oscillator on the Voyager. Then there’s the Bass Murf - have you listened to the demo video on Sonic State of that? Sounds awesome!
But I’m drifting off-topic so I shall stop! 
I have an MF-102 coming this week… am start to get obsessed as well. I’ll check out that vid now.