After putting my bike together, I rode around for a couple of weeks without brake sensors. I have to say that the sensors are a very valuable part of the system - they make riding much safer and more pleasant and even extend the battery range. They work well and seem stable now that they're on, but I removed one star because they were pretty fiddly to install. I didn't have too much trouble getting the distance right, like some previous reviewers, but they were not well suited to the shape of my brake levers (Shimano deore XT), so a lot of glue was required. If you have these I don't think a gear change sensor is required, because the brake sensors can be used kind of like a clutch, switching the engine off momentarily while the gears change.