I believe it uses JFETs as voltage controlled resistors, which could be tricky. Don't think they set up as differential stages, either.
I had one for a short time and didn't really like it. Audio quality was OK. Not much distortion. Problem was it didn't sound like the LFO was balanced and perhaps the range of variable resistance was too high. It more resembled the seasick, out-of-tune sound like a BBD vibrato rather than a Magnatone vibrato to my ears.
To me, the Magnatone sound is closer to a harmonic tremolo, but heavier on the phase shifting and lighter on the amplitude change. Possible my unit needed better adjusting. I didn't tinker with It other than taking a look inside.