As part of my ongoing research project to buy every autopilot out there and see how they work (an expensive hobby!), I just got a FY-21AP, which is a $250 stabilization and RTL box (basically an autopilot with most of the usual features taken out). (I bought it from HobbyKing for $195, but as Hooks warned us that didn't last long. It's no longer available from HobbyKing.) You can read Hook's introduction to it (and links to reviews) here, but I just wanted to point out some cool things that caught my eye in a quick unboxing.
First, it comes with a really neat vibration isolation "hammock", which is the little platform in the picture above with rubber bands on all four corners. That's a great way to dampen vibration; we should make and sell one of those for APM, too.
Second, here is the usual warrenty-breaking opening of the box:
It's got the same ST ARM chip and ST sensors as all the other FeiYu boards, with a barometric pressure sensor in the bottom right of the board at the top. A neat, simple design. It uses a Locosys 10Hz GPS with a small ceramic patch antenna.
There is no provision for a ground station or any desktop setup software (although you can hook up an optional OSD and see data in the video stream). All adjustment for your airframe must be made via the little trim pots. It can handle elevons with a jumper, but not V-tails (you need to use an external mixer for that).
There are three modes: stabilized (optionally with fixed altitude), return-to-launch (RTL) or circle-in-place. They are selected with two toggle switches on your transmitter.
Throttle is not controlled, and altitude is only controlled with the elevator, so the manual warns you to keep your throttle pretty high to avoid stalls in auto mode.
The documentation is much improved from the previous FeiYu Tech manuals (which were partly in Chinese) and comes on one big double-sided sheet of paper:
I haven't flown it yet, but I'm guessing it a does a pretty good job on most aircraft. If you don't need a full autopilot with programmable waypoints and ground stations, etc, this seems like a fine choice. In particular, it seems really well suited for FPV fliers to protect against getting disoriented and having trouble making it back home.