Here's the way I see It.
You find a rat toilet or feed bed and you set them. Now your only going to catch ONE rat at those locations. But If you make several lured sets close by those locations your going to catch more then ONE rat. Those feed beds and toilets are being used by more then ONE rat.
Must be different rats over there, Beave. I catch rat after rat on feedbeds and toilets (no lure/bait). I'll take a feedpad over a house any time. Yes, some are one or two (like huts) but just as many are 3 or 4 or 5 rats using that pad. And if that one runs dry quick, another one has usually popped up so it's just a matter of moving the trap. A feedbed is usually much faster to set than a hut, too.
By the time you dink around with rat lure, you could have set another trap. Not to mention tracking down coon that are also attracted to rat lure (probably more than a rat is). And be sure your rat lure doesn't have castor in it (some do). Then you have the issue of beaver in your rat traps.
I quit using rat lures years ago. My catch didn't go down, it went up. That said, every location is different. I see a few places every year that a rat lure "May" help. But those are also coon locations...sooo.
PM me for the best float bait I've used in the dakotas Youthtrapper. Nobody has ever touched on it here. Carrots are a poor rat bait, IMO. They do attract rats, but rats really don't like them once they bite into them much...which granted is usually too late.