The limo liner offers travel between Boston and New York. The amenities are comparable to the train, but just like any other bus, it has to contend with traffic.
Also, if you notice the departure times skirt rush hour times. There's no 5pm bus, for example.
Given the similar pricing to the regional trains, the only real advantages are the internet service, which is a shared satellite connection and a 1 seat ride from Framingham, MA. Picture 20+ people sharing a single DSL modem and that's about what it would look like.
As far as I know, the service is well run and comfortable, but I'll stick to the train. The scenery of the Connecticut coastline in the morning appeals to me more than the "scenery" of I-90 & I-84.