I wanted to keep my original tips when I had my Magna Flow installed. The guy at the shop said that the original pipes were smaller and he would have to make an adapter. This would restrict the flow and change the sound.
He also told me that with the adapters on, the tips would stick out further. After a while of owning it, you don't even notice it. One thing, if you have a roadster, the exhaust might bang into the underside braces. This can be solved by using a large tie-wrap around the exhaust hangers at the back of the car.