It doesn’t really, though. The formant stuff is largely useless without software that Yamaha never released. And you can’t really program the thing from the front panel at all, so you are much better off just using a VST.
It’s pretty, and a nice collector’s item though.
If you want weird robot vocals, the Monomachine’s VO synth is much better. If you want more conventional vocals, the CT-S1000V is much cheaper than either MnM or FS1r and is still in production. If you just want some funky formant sounds, any synth with two or more parallel bandpass filters will do the job.
(I’m a bit grumpy because I paid $800 for mine, which was a steal at the time, but was so disappointed that I ended up giving it to a friend for free. Felt bad charging for it)
Edit: MODX has 8 ops and a MODX-6+ sells new for less than what Reverb sellers are asking for a FS1r.