I upgraded (1) of my (8) IP3M-941's to the new firmware. Ran into some minor problems with PTZ, and after trying some workarounds decided to "downgrade" back to old firmware (I had a copy on my PC). The downloaded files don't say anything about not being able to downgrade, and I hadn't been on the forum to see the warning at top of this thread.
The "downgrade" appeared to go just fine, but the camera didn't reboot. Solid red light on back. Powered off, back on, solid red light -- no movement, no network connection. Held button 30 seconds - nothing. Held button while powering on, got a few flashes of the red light, but nothing further. Tried multiple power cycles and hard resets, no response -- just a solid red light. CAMERA IS DEAD.
I RECOMMEND HEEDING THE WARNING IN POST #1 OF THIS THREAD, AND DO NOT ATTEMPT TO DOWNGRADE THE FIRMWARE. The camera I tried that on is now in the TRASH.

As to the rest of my experience with the new firmware....
#1. The old firmware positioned the camera to preset #1 after reboot or power cycle. The new firmware seems to position the camera to the "last position set using PTZ jog controls" -- even if a preset was chosen after that. Would like to see the old behavior restored in a future version, i.e., go to preset #1 on reboot or power cycle. (There is a workaround for this in BlueIris, using the "Watchdog" function to select preset#1 on signal restoration.)
#2. I had terrible PTZ delay, overshoots, and some trouble setting presets when using EDGE browser. Switched to CHROME and had none of those problems. Using Chrome, I was able to set/delete presets reliably, they were retained after reboot, video and PTZ were very responsive.
#3. PTZ presets and jogging initially did not function at all from BlueIris. Changing the BlueIris setting for PTZ type from "Amcrest" to "Amcrest/Dahua" resolved that. Using the new setting, PTZ jogging and presets worked perfectly from BlueIris and were just as responsive as with old firmware.
#4. Really like the UI being native in browser (javascript)! Will be glad to ditch the plugin!