I've done a twelve mile walk easy in my tay muck boots, with no issues. I have a fairly chubby calf so I like the neoprene, and they are warm and comfy as anything. I reckon I'm in mine for about 10 - 15 hours a week and I haven't had a problem yet.
They seem expensive but given that I wear them much more than I would a walking boot, and given that a decent walking boot is probably over a hundred quid, they aren't really all that bad value at seventy quid...