My wife and I are both participants in SOTA. She is strictly phone while I am primarily CW. We have had summits where she barely made the four contacts needed due to conditions.
I purchased one of the MX-P50M amplifiers and did a few bench tests. The device used for amplification is robust and capable of 100 watts at 900 MHz. The output is clean as long and you have the band switch set to the correct band. It functioned from 10 to 15 volts, the PA could take more voltage but I wasn’t sure about the rest of the circuit. The output power using 5 watts drive, varied from 35 to 45 watts, depending on voltage and bands.
We take it up on the hills and she now regularly makes 10 or better contacts. We use a 6 Ahr LiFePO4 12V battery, which seems to be all we need, so far we have activated three summits on one charge and the battery had plenty more to offer.
So far 70+ activations and no issues.
By the way, there is a SOTA Reflector thread with how to connect the FT817. FT817 + 45w Amp cable info needed
Lee N7LP