I've been on it a couple of times. Pre-booking is a bit of hit or miss as sometimes they let you book and sometimes not. They'll drop you at Mochit BTS if you ask, or take you to the bus station, but nowhere near where you'll catch a departing bus from and it took a bit of finding the first time for me.
They've also got a couple of bus sizes and I feel a lot safer in the bigger ones.