Per the ARRL September QST the uBitx v5 passes FCC requirements. The prior versions did not.
Other than cleaning up the signal, there are only differences, not necessarily improvements in the calibration procedure. Calibration now requires a dummy load, or else you would be transmitting on 10MHz, out of band for the US.
I do feel like I can now build the 70 watt linear for the rig that I was hesitant to do so with the prior versions. After that will go back and work on the 2 v4 rigs that I have to get them up to speed and setup for digital.
Really fun rig, and a good platform to learn on.
The above is my opinion, others may differ and are entitled to their own.