Is it possible to downgrade from 1.4 back to 1.3 or is it complex and difficult that it would even cause more problems?

Procedure is the same as updating, however it doesn't fully downgrade all modules that were upgraded so I'm unsure of the benefits or issues that result from doing so.

Especially it does not downgrade the ESC fw which is the biggest problem but with 1.4 you should still not have problems.

Their advertisement that you can downgrade firmware is simply not true but you have to be expert to find this out as on the screen it will try to tell you that it did downgrade. In reality you have a hybrid version then.

I just went on and upgraded everything to 1.4. Tested last night no issues but that was just a small test flight. I'll do a serious test flight when weather is permitting.