Most EV conversions end up keeping the manual gear box because it's simply easier to build an adapter plate for the motor transmission interface than it is to build out a whole new gearbox replacement.

From what I've seen it's fine, you can choose which gear to shift to and leave it there. Cold start from 5th gear. Can even be fun to play with the gear ratios, apparently. But it is another point of failure.

One of the things holding me off from attempting an EV conversion on my old Saab 900 sitting in my shop is that the gear box in it is notoriously brittle and would break even with the torque from the (turbo) gas engine that it shipped with.