I'm only biased because they're better - no commercial affiliations with any roof bar manufacturer.
I've got some very similar to the Rhino 2 bar system - I can't remember the make offhand, I'll check the garage tomorrow, but mine are a 2" square tube with a welded plate style adjustable end plate gutter mount that attaches with 3 bolt clamps. Unshakeable things, if the roof was strong enough on a defender you could lift the car with them.
They are heavier than a set of Thule bars, but a) its a Defender, you'll not notice once they're on and b) try standing on a set of Thules and you'll definitely see the advantage of the stronger bars - you can get roof tents for the Rhino style bars, not sure I'd want to do that on Thules.
The Rhino ones look to be about the same price mine were new - in the order of £100 to £120 anyway. Ebay is your friend