I have just been looking on the smart trike website, If I were to buy one, (the grandparents bought this one, on special I think) I think I would go the deluxe model, its probably more exxy, but I think it would be worth it.
It has rubber wheels, which would make it a more smooth ride, less noisy, looks like this is the one that comes with the phone.
we have the basic model, or "classic" and it can be a bit bothersome to steer, the plastic wheels are noisy etc, but like I said DS does really like it.
check out the website, they have lots of different models with all the features etc.