As Patrick has experienced, the rig works very well even if it looks a bit unusual. The only thing I have found is that some poppers don't swim as well as they've been designed with trebles off the belly and the weight off the head can have a detrimental effect on the action, particularly in less agreeable conditions. The Cubera is a popper that works well with this rig though.
I agree with Patrick that a slightly longer assist than what I have in the photo is desirable.
In terms of weaknesses on this rig, I have mentioned the potential balance issue above. The only other thing I would mention is just an observation more than anything else and that is that I have seen a number of occasions where the hooks have been straightened out. I suspect what is happening is that the GT is hooked with both the head and tail hook and the fish is able to work the hooks against each other. I think you can compensate on this to a degree by adding a second split ring to the tail hook. I know Glanville Heydenrych from Nomad who I regard as one of the best GT guides on the planet suggest using only the assist hook - yep, one hook!
On your comment about the belly swivel being compromised on the Heru, this is a rare but unfortunately not unheard of issue with the Herus. If however you buy your Herus from the Kaiser Pro Shop, you mitigate this issue as from what I can see, their lures are specially made with what look to be Sasame swivels. Of course, if you use this rig, the belly swivel is redundant.
