I'd say to try to find an owner nearby to let you check the J30 out. It's not inexpensive purchase, so best to know what you're getting into.
Wish I had feedback for the RTT, but I've only had ground tents and the Ursa. For me, clearance is a big issue, as I daily drive my Jeep and short garages are everywhere. I could not fit in many of the carports or garages I need to with a RTT on a roof rack.
Getting in and out, you have options with the Ursa to do it from inside the Jeep, or do like some other folks do and run a ladder up to the exterior like you would a RTT. With two people, it might be a bit of juggling to open and close a hatch when you want to get down. In the cold, I appreciated being able to dress in the hatch and put my boots on in the Jeep before getting out in the cold.
Weight is probably a wash when you add in the rack. Drag is going to be much better with the Ursa. Cost difference will vary wildly, but you could come in well under the J30 with the right combo of rack and an inexpensive RTT. Not sure if you'd install yourself or have it done at the facility, so that's also a wildcard. I watched the guys do it in San Diego and while I think it's not insurmountable to do with a friend or two and a hoist, I was more than glad to have the guys there handle it.
Given the choice to do it over, I'd buy the Ursa again without any changes.