I don't have the platform, but I have the Backbone System with 3 cross bars setup on my JKU. My Jeep is at stock height with stock wheels. I own a Treeline Outdoors Tamarack, which is lighter than most out there at around 120 pounds. I also put a 42 pound Batwing awning up there too.
Cons:
Mileage - I get 14 liters/100km without anything up there. I get hit with a 2 liter penalty for keeping it up there when highway driving.
Noise - More wind noise.
Freedom Panels - even though they come off, too much wind is directed right down on to the center of your head. Fine for anything less than 50 km/h, otherwise too much.
It's still a tent - You can't really put it away wet. Ideally you dry it out before stowing, but sometimes you simply can't. Unless you have limitless garage space. Don't forget, cooler months = condensation.
Can't take anything other than the tent - no room for kayaks/canoe.
Pros:
Modularity - Can reconfigure fairly easy depending on what you are doing. Tent comes on and off fairly easy now that I have a routine. I change it out for transporting 2 kayaks, use the cargo basket, or strip everything off if we are doing a longer, non-camping road trip.
Top heavy-ness - It's not that bad. I thought it would be worse. May have something to do with stock height/suspension.
Comfort - We sleep 2 as well as 2 40 pound Springer Spaniels in comfort. I don't think the Ursa Minor is as wide/roomy, though I could be mistaken.
Inherent awning/annex - gives some additional living space when needed. Though, more wet stuff to deal with when it rains.
That's all I can come up with off the top. I am supposed to be working, Monday motivation is hard to find.