As someone who works with ArduPilot professionally, I have very mixed feelings about it. It’s mature, definitely. It supports all kinds of vehicles, like you say. It’s beautifully modular and supports a crapload of flight control and sensor hardware. And there are definitely pieces of it that are aggravating and exceptionally janky.

The HUD overlay you’re referring to is technically Mission Planner (GCS software), not ArduPilot (flight control software). Mission Planner and ArduPilot both talk Mavlink, and they’re both developed by the same community. MP is flexible. You can set it up to do almost anything you’d ever want. It’s also terrible and exceptionally janky… but extremely powerful. And they’re both free.

I think the problem with both of them is that they’re good enough that there isn’t likely to be a huge critical mass developing a better alternative. On the GCS side there is also QGroundControl and APM Planner 2 (which was a fork or reimplementation of Mission Planner). Both of them have their own upsides and downsides, but neither one of them is as mature or as powerful/flexible as Mission Planner. PX4 on the flight controller side is popular commercially because it’s BSD-licensed instead of GPL, but the net result is that it has nowhere near as many features as ArduPilot because companies build proprietary features and don’t push them back upstream.

This stuff is definitely in the worse-is-better domain. ArduPilot is free, ArduPilot is amazing and ArduPilot sucks. :)

Anyway, off to bed. I’m in a long test campaign right now and we’ve got to be up at 0430 to fly the ArduPilot-based aircraft again before the weather goes sideways.