I recently bought a P40C to run with a pair of Viper 15 ESCs and no amount of effort would get the Viper to behave, it all worked perfectly except for left rudder while reversing when both motors just stopped. Changes to the set-up merely altered which command option failed.
I had not bought the Vipers from ACTion and had foolishly not asked if they were compatible with the P40C, nevertheless I emailed Dave at ACTion-Electronics and got an immediate reply.
It contained some suggestions that may have solved the problem and a clear example of great customer service too, Dave offered that if the P40C was incompatible, then I could have a full refund of it's list price against a P94 combined Mixer/ 2*ESCs. I posted the P40C back on Saturday and received the P94 on Tuesday.
A brilliant company, there is no better example of a company looking after it's customers ( Even idiots like me )
Now I have got 2 brand new vipers to sell on Ebay !