They isolate a little bit better than the THX00 does as far as leaking sound in. They don't leak sound out. They're somewhere between the THX00 (and all similar designs) and the ShureSRH840/Audio Technica M50/M50X in terms of isolation.
To me they're a good compromise for most mobile situations. They allow you to hear your music and not bother other people, but you won't get run over by somebody honking their horn at you either. I like them for things like riding a bus, where I want to hear what's going on, just lower. But they're not good for plane travel or drowning out a loud office, but I only really use IEMs or noise cancelling for those situations anyway.
THey're good for what they are, IMHO. They're not giant killers. They're not isolation monsters. They're a cheap-ish, good looking, non-offensive, fun headphone. For $75, needing a smaller closed can, they're amongst the best you can buy. I think they're more durable than people would give them credit for. My old Denon D1001 has lasted for 10 years. And i threw that thing in a backpack or briefcase daily for at least 5 years of that time every single day. The only thing that has happened is that the pads have started to flake a little bit, which is totally normal for that time frame, and that price level.
These comments were based on owning the Walnut (and also D1001), btw. But as far as what I said above, it should all equally apply.