Knowing Sony's previous engineering feats in the tape-recorder field (from the TC-D5, to the TCM-100, pro RtR or... video), the TC-FX7 wasn't all that impressive, even if... impressive.
Slim as can be, only a centimeter and some hairs taller than a cassette itself, thanks to its miniature S&F head fixed directly onto the REC/PB circuit board.
The motor is Sony's staple Quartz-locked BSL (brushless, slotless linear torque) centered on two samarium-cobalt magnets and mounted directly on the Quartz-locked drive capstan.
Feather-touch pads and a digital counter with memory add convenience and precision ; the B Dolby noise-reduction is done through Sony's own Dolby chips - of course.
Adding Dolby C and a third head would probably have made, then, the TC-FX7 more palatable to high-enders :-) But an optional RM-80 IR remote or RM-50 / RM-65 combo could make up for some of that - discretion and convenience !
The FX7 was built at the Sony Tsukuba factory (Sony TB).
I have the pleasure of owning a TC-FX7 which I use in alternance with my TC-K88B. And a TC-FX1010. And a TC-20F. And a TC-100A.