The nuppin' is about the same diameter as the RM4, so smaller than the 22mm atties. It's great for flavour. A little quirky to build at first, but worth the time investment to figure out. There's a good active thread in here about it.
Of Rob's 22mm atties, I'd recommend the RM8 (derringer). RM6 & 9 are slanted more towards bigger air, while the RM7's chief selling point is top air flow (resulting in it being virtually leak proof). The RM9 has this feature, too.
There's nothing wrong with any of them - they're all good atties - but if you're prioritizing flavour above all else, the RM8 would get the nod (IMHO, of course).