Mirrors legal requirement, not everything gets checked on an MOT. Can be a life saver, any mirror better than no mirror.
I ditched my mirrors on the Panigale V4S after having it for 3 weeks. They are worse than the RSV4, they vibrated but no where near as bad as the Panigale. And at least the RSV4 mirrors folded. I run one bar end mirror on the right side. And i use DB Racing mirror blank/indicator combo. A pricey but really nice and well made piece of kit. (Those are still removed for TD's though).