Well I tried it with the bubbly hot milk and butter and you were right, there are no lumps. The only problem is I don't know that it's any easier than whipping out my mixer and, as opposed to some opinions here, I do like my potatoes whipped up with my beaters. When I use my beaters my potatoes don't harden when I put the leftovers in the fridge.
I just find it so much easier and faster to get my hand mixer out (I don't have a stand mixer, no room for it) and whip my potatoes up.
I do think I will love my ricer for straining spinach though. I'm going to try that next. I'll let you all know how I like it.
Thanks for all the replies!