I’ve used the cover a lot. It’s a hassle to use, but sometimes it’s necessary. I have no regrets getting one.
I have dynamo lights, but the lights are much lower than I’m used to on other bikes. I attached a Radbot 100 rack mount using zip ties, to tabs on the the underside of the Brompton saddle.
The saddle gets in the way of mounting a Radbot 100 (it’ll fit, after a bit of pushing). But it is just possible to mount and unmount a Planet Bike Superflash because of the indent on the Brompton saddle (it shares the same sized mount with the Radbot).

The screws in the picture don’t actually hold anything in place.