Interesting thread. I too was entirely ignorant of these transistorized balance movements until I bought one and subsequently serviced it. This one a Seiko Elnix from 1974 featuring the 0703A, the last in the short line of Seiko's electronic balance movements.





I somehow thought these would be flaky and unreliable, but since completing the service back in May, its been running sweetly at 28800 bph and doing so with the most amazing accuracy. I made a short video of the movement in action here:



If you are interested, you can see the write-up of the service here.

Martin