As Mojo stated, plus has little to no maintenance. No changing shift cables when the mechanical shifting starts to suffer. Shifts as well 4 years down the road as day 1. Not cheap, if you can get a bike with it at a good price, it’s worth it. I have 2 Di2 systems and one SRAM AXS. On mt. bikes it’s arguably a better choice as I find I shift a lot more often then on my road bike and every shift is dead on perfect.