Copter-4.2.1 has been released as the official/stable version and can be installed using MP, QGC or it can be manually downloaded from firmware.ardupilot.org.
The changes vs 4.2.0 are in the ReleaseNotes and copied below.
- CAN ESCs bus bandwidth efficiency improvements (see CAN_Dx_UC_ESC_OF parameter)
- DShot timing improvements to support more ESC variants
- LOITER_TURNS command radius max increased from 255m to 2550m (but only 10m accuracy when over 255)
- Luftan EFI measures fuel consumption (see EFI_COEF1, EFI_COEF2)
- Bug fixes
a) CAN ESCs work on boards with no safety switch (e.g. MatekH743)
b) Inflight Compass calibration checks GSF yaw estimate is good
c) LOITER_TURNS command’s Turns field limited to 255 (previously would wrap to lower number)
d) NeoPixel colour fix
e) Precision Landing maintains yaw during retries
In general these fixes are pretty minor and won’t affect most users so feel free to take your time and upgrade when it is convenient.
All required parameter conversions are done automatically so in general there should be no need to back-up and restore parameters or re-tune the vehicle after this upgrade.
Thanks very much to those who contributed to the beta testing of this release!