To bring a land-vehicle onto the island you need prior permission from the Traffic Committee. Don't make the mistake of buying and shipping something and then not being able to bring it on the island. To get permission you will need to be a resident, and the kind and size of vehicle will need pre-approval as well. Much better for you to come down, get yourself settled and then address the vehicle issue. If you personally are not allowed to import a vehicle then you can probably make arrangements with somebody who has one on island already.
When you buy and ship there's no way you can realize the benefits of any warranties. That is another reason to try to buy here.
The other thing is that generally (not always, but usually) the things you buy here are things you can get fixed here (parts etc).
If what you want is already here I'd say buy it here - depending on the item you might even save money doing so.