I think I've commented on these before. Each has some design issues that have to be considered, too.
For example, Duffer's model has a trigger that must be "pulled" so if the trap is bedded into, say, a soft creek bank the trigger is pulled back out toward the hole by the coon in order for the trap to fire. Its something to consider, anyway. You really have to get that trap solid into the bank so that the whole unit isn't worked free by a coon while they are working the set. These models aren't hard to set, either, but do have a separate pin and cotter pin arrangement...so don't lose any pieces while you are setting them in the field.
Coon cuffs have a trigger that is pushed away from the opening, make them a nice choice for bedded situations. You can also use a bigger hole behind the trap with bait, lure, etc. and the trap covers up the opening. These traps also fit nicely into the end opening of a 4" or so short section of PVC pipe, which you can plant into the creek near a trail.
Both traps work well on drowners, and both are very pricey compared to comparible sized footholds.
I've caught many possums in the duffers model, and only one in a coon cuffs, model, but none were target species catches for me. I'd say yes they should work well for possums for you. I used smoked salmon and fish oil for bait on all those possum catches.
Never tried the griz models....
I use the dog proofs in couple of areas where I am limited to no footholds (dogs, cats, etc.) and probably could have caught way many more coons with footholds but again the owner limited me to these traps. I've caught a number of large coons in them, so wouldn't hesitate on holding power of either model.
The rubber hose spacers on the older coon cuffs models did break down with age and when dipped for me. The Duffers models need to be cleaned out immediate after season or they will rust inside where most of the critical parts are, too.
Just my two cents on them anyway...
jim-NE