Some thoughts after extensive testing of the flashes.
Quite like this small flash 2 x AA cycle times are faster than the F20M and it's far more versatile, except it can't do the TTL Optical Wireless which probably won't be a problem as it's got the radio build in. Controls dead easy LCD is also up to the job the radio works without issue even at longer ranges with the X Pro controller. I don't like the AF assist light it's a big orange circle with a larger circle on the edges it's pretty bright, not as effective as the AF beam pattern off the 685S. It works but it could annoy people with the brightness. Output is good fair bit more than the F20M, obviously not as powerful as the bigger flashes but good enough. Also has HSS, but limited range due to power still worth having just don't expect fill flash group shots. Build is nice enough it's also compact so that it will fit smaller bodies well or work out if you just want to take one flash and cut down on the bulk for a day trip. It won't replace the 685s, but will do the job in many cases or work as a second flash pretty well
V the F20M a no brainer really if you are using radio which means no need to worry about the master/slave situation on the Sony wireless flash. It has S1/S2 slave modes so you can use it as a simple off camera flash if needed. Biggest downside to the F20 is the no rotation making it very limited in use, and the no manual mode again limits the use of this flash... there is no reason to buy the Sony flash with this one around. I didn't pay for it... I swapped it for another flash I had not sure I'll keep the F20M as I don't use it much. Godox just brought out a Li-ion version of this but I'd stick to the AA myself same as the 685 I prefer it to the 860II despite slower cycle times they are fast enough for most.
Part II coming soon...