Rode one of these (22") a week ago for a brief test drive. Took some getting used to the 4" tires and how soft they were. Handling, accelerating and maintaining speed weren't all that much fun. But that's not what it's about, it takes to the off road and normally unride-able surfaces and obstacles like riding over curbs a cinch though. Tires weren't really knobbies, but had spider patterns on them.
The one I rode was loads of fun in terms of going anywhere. I saw a video of the Surly Pugsley riding thru top bar submerged deep water, that thing will float too. The place I test rode it at was an X-Games store in Port Orange, FL, they had a pool, but I wasn't dressed to ride the bike into the pool and tried to float it or see how deep I could ride it ? Maybe with a snorkel or scuba, you could go really deep with it ? Had I been prepared & allowed to, I would have tried the pool out too.