It's more work, as you not only have to put it together, you have to paint and detail it as well. But that's what some guys like. I did a Ferrari 250 GTO kit MRRC put out, which is similar to the 275 kit as far as the chassis goes. The chassis went together fairly well, but you do need to have patience. I had an old Revell body that fit right on, so I haven't done up the kit body yet.
I highly recommend getting the kit. Don't think it's any "faster" the the RTR car, but just the satisfaction of putting a car together with good quality parts (ex.-aluminum wheels) is worth it by itself.
BTW-anyone know where I can get the King Cobra kit? In the USA?