I think we should know about the limits of a one eye byakugan/sharingan of the orginal/donar user. I mean can byakugan give almost 360 degree vision to the user with 1 eye? if yes then I wonder if the 2 eyes can perfectly combine their powers togather, to be like you know a full 360 degree vision with full clarity “From the sharingan” and the ability to react to everything even from attack’s from behind with ease “but of course. within their physical limits”.
Combination of Tactics like, The uchiha Clan shuriken ability which is already increased with sharingan clarity can be even more enhanced by the byakugan with them being able to see through the blindspots easily.
They might as well be able to shoot needles at the exact chakra points of the opponent by the ability of the sharingan giving accurately shoot at the chakra points or nerves (like-Haku)
Maybe even be more better with the sharingan genjutsu skill.
They can probably hide in a far away place and use the far distance sight of the byakugan and see through other shinobis jutsu without them even knowing.
Well drawbacks would probably be that they can’t actually use the each eye to the full potentiel they do as a pair of one type of eyes.
hmm with one of them evolving as a MS (Mangekyō Sharingan) would probably depend on which MS (Mangekyō Sharingan) we are talking about like, if it’s Itachi/Sasuke’s then they probably could use the Ametaresu at a great distance and even without staring at it like cast it behind them. since its cast by whatever the user can see and thus the ability of the byakugan allowing everything to be seen each side and at a great distance. And long distance Kamui being increased the same way too.