I had one on the Silverado that I no longer own.

Pros: It looks fairly nice; it's rigid; it locks pretty securely; it locks in various semi-retracted positions -- useful for still covering up some stuff while hauling larger (taller) items in the back.

Cons: Despite rigidity, it still sort of bounced up and down with the wind at highway speeds; the top rolls up into a box that's mounted in the front of the truck -- I felt like that box took up too much bed storage room; the front and side mounts go over the bed rails, which prevented leaking, however, where it meets the tailgate it doesn't go over the top -- just has a rubber gasket that presses against tailgate -- I did find that this leaked some in the rain; also, that gasket had a tendency to come out requiring manually fixing it back in place -- which wasn't easy; the top rail edges that cover the siderails which I mentioned above permanently blocked the stake holes, so I couldn't mount tie-down attachments in the stake holes; the lock is facing straight up -- it would get wet and freeze in the winter -- probably need to find a lock cover, plus keep it lubed; there's a little plastic switch underneath that needs to be pulled-on to allow the top to be extended from any locked position -- be default, there's this big nylon strap that screws into that switch so you can pull on the strap to disengage the lock -- well that strap is always in the way, plus one of it's plastic attachments broke early on for me, so I just got rid of the strap all together -- however, unless you have full-length side rails, or have pretty long arms, it can be hard to reach that switch without the strap on it; the back end of the rails have little plastic caps that prevent the top from extending too far -- those little plastic caps are held in place with screws -- one of my caps broke within the first week and I had to make a point of not pulling the top back to far when extending.
Bottom line: I don't mean to sound overly negative about this thing. Given the other available options it might be just the thing for you, but I'd suggest you find one to look at before buying it. Of all the above negatives, the two that stand out are 1) loss of storage space because of the collection box in the front which the top rolls into; 2) leaking at the back end. Also, take this all with a grain of salt, 'cuz I'm not a big gizmos and gadgets guy -- I think most of the bolt or stick on accessories available for our babies (I mean trucks) aren't up to the overall quality standards that I'd like.
Here's a couple of pictures of mine if it would help:
http://jeffmarrs.com/truck/jackrabbit.htm