The “Mark 2” SCU was from about 10 years ago (we’ve been doing this for a long time!). Although we’ve never had a single complaint, it did fit a lot of functionality into a very small space. To the right of the main joystick are two momentary push buttons (for vertical / heading hold, etc.). We stopped selling them a long time ago. The new Mark 4 is a much simpler design and is my personal favorite of all those I’ve used.