Let me preface my review by saying that I've only tried this service once, as a tourist going on a…read moreday trip to Oxford from London. My comments below may not apply to what I imagine is the core of their business, the Oxford-London commuting run.
I was going to Oxford to visit some family friends with my mother. My mother organized the trip, which was, of course, my first mistake. Never let your mother organize any part of your life: one minute you're living the high life in London and getting her to organize trips to Oxford, the next minute you're living in your parents' garage married to some family friend's comely daughter and wondering where it all went wrong.
I personally thought the train would have been a better deal, but anyway, on the bus we went. Big mistake: instead of taking 1-1.5 hours to get to Oxford from Victoria station, it took more like 2-2.5. This was due to traffic (hardly surprising) and the fact that the bus took an absolute eternity to process passengers at each stop.
On the way back, the bus broke down and we had to wait for a replacement bus to come by. This might have just been luck of the draw, but this bus route is highly competitive and I suspect market forces compel the bus operators to minimize costs as much as possible. Combine that with the fact they run 24 hours a day every 10 minutes and I'm sure you get quite a few breakdowns.
And then there's the price: a day return was 16 pounds a person. I priced the London-Oxford train (which takes about an hour), and a day return was 20 pounds. If you have a network railcard (you do have a network railcard right?), this drops to 13.20. Sure, the bus has wifi and the train doesn't, but from my experience the wifi was very unreliable.
I'd stay away from all bus services to Oxford unless you have a good reason not to.