I went from the 3pv to the NB4. For me the NB4 has better ergos, much better interface, a higher quality feel, and smaller receivers. Oh, the USB interface works really well with VRC
My NB4 is set to 1 way communication for lowest latency, I cannot tell a difference in response between the 2 radios. I do not have the dead zone problem on my 3 month old NB4.
Downsides of the Flysky is that it's made by Flysky. I do not expect good support or parts availability. No problems so far though.

I've not tried a 4pm for comparison.