I like the lower clearance of the Frontrunner. I went with a Baja, which is extremely rugged, but a little higher. It has side rails, etc. so it is quite a bit higher, maybe a bit more rugged.
Low profile is one reason I chose the Hannibal over another Safety Devices when I bought the Discovery II and later sold the SD rack but still have the Disco I
For the Disco I and II, the Hannibal mount system is very well built and about as rugged as I think aluminum could realistically be made. However, that is on the gutter mount of D1/2.
The LR3/4 with it's few roof bolt points, and/or factory tracks, does not lend itself as simply to a rugged rack mounting. Almost all I've seen use 6 points on the rack itself and the factory tracks maybe mount into 8 roof holes (? 3 per side mid roof and 1 per side up front beside the sunroof)
So far my "temporary rack to vehicle interface has worked since 2007 and it's just 3 Yakima cross bars set into their own bases which are bolted into the tracks by 2 4mm bolts each base.
This allows the entire rack and the 3 bars it is mounted onto, to be lifted off in 5 minutes by two people. Alternately, I can do it solo by unbolting the rack from the 3 bars (6 x 3" bolts top down from original rack holes and through drilled holes in the cross bar ends), then remove the bars individually, or leave them if needed for a roof cargo box or super simple roof tent mounting.
These 3 bars ended up working so well, I just kept using them

I also like that if necessary, I can solo dismantle the entire system as well as it's modular multi-function.
The same ideas could be applied to Front Runner very easily, or other brands.
Oh. the space created between the rack and the factory tracks, allows my fiberglass waffle board/bridging ladders 12"x48" to sit cross-wise track to track just above the glass roof. There is space for 4 but the plan is for just the 2 waffle and a couple nested aluminum sand ladders.