Amazon shuttle from Everest to Doppler

How is the shuttle service from Everest(Bellevue downtown) to Doppler? Can it be easily used for commute? Or is it always filled and you have to wait for the next one(30mins)? I heard you cannot book your spot and hence I am not sure if I can rely on that. I am looking to stay in downtown Bellevue and not sure if there would be any vanpools/scoop options apart from this shuttle. How is this commute in general? Any pointers would be very helpful.