the G505 which was a Strat style with three guitar pickups.
The biggest downside of these early guitar controllers was tracking. If you played too fast the synthesizer could not read the signal in real time. There was definitely an art to playing these early instruments.
They also produced a stand alone version of the GK-1 that was sold separately and could be mounted on any guitar to make that guitar into a controller. This has evolved into the modern version called the GK-3.
For example you could play a chord on the bottom three strings and press the hold switch to sustain the chord. You could then play a lead part on the top three strings.
Whether it was useful or not...who knows? But it sure looks cool!
For this series Roland also developed a bass synth controller called the G77 which matched the bass synthesizer, the GR77B.
Here is The Guess Who with Randy Bachman playing a Roland GR505