As with most Yamaha gear of the era the CS70M is an extremely well-built and reliable Synth. The controls have a solid, quality feel you would expect of a high-end Synth targeted at the professional market. The front panel function set is pretty much identical to the CS80 except there is only one set of controls that toggle between the two channels. Yamaha CS-series Synths have a unique dual single-VCO architecture and this - though lacking the weighted velocity keyboard/polyphonic aftertouch/pitch ribbon of the CS80 - is the most advanced in some ways with programmability and keyboard split function. While it doesn't sound identical to a CS80 it is still a big-sounding Synth and is about a third the weight at a somewhat more manageable 85 lbs. The high prices these usually sell for reflect their scarcity and vintage collector's status as well as it's kinship to the much more expensive CS80. You probably wouldn't want to get one of these as your first analog PolySynth but if you have the finances and opportunity to purchase a CS70M it could make a unique addition to a serious Synth arsenal.
Prophet 5 rev.2, Pro-One, Juno 60, Jupiter 6, Matrix 12, OB8, MS20, Poly 800, CS70M, DX-7, CP35, Casio PX-5S, Hammond C3/M102, Vox Continental/Super Continental, Gibson G101, Farfisa Compact, RMI 300A, Pianet N, Combo Pianet, S770, S760, S50