After using the Jimi "wallet" for a couple weeks I have found that it does serve a few really good purposes. The thing that works best for me is as a cyclist it's small compact and fits into my jersey pocket without being bulky like my wallet used to be. It also keeps the stuff I have it dry when most everything that is in my jersey pocket gets covered in sweat and it's nice not to have to put something in a baggie. I also liked it's size when just carrying it around in my pocket I hardly new I had anything in my pocket. I also felt that I didn't have to worry about anything falling out everything is enclosed and secure. The only problem with it is that it doesn't allow you to carry as much stuff in your wallet as I usually do. It did make me take a look at what I had and what I really needed to carry but still seemed a bit small when carrying just the cards I needed and some cash.
Overall I found the Jimi wallet to be nice and will always be found in the pocket of my cycling jersey plus it's kind of interesting and people always wondered what I was using. My son also thinks it really cool and I'm probably going to have to get him one too.
I have to start off agreeing with Harp totally. I tried my bulky leather wallet in the jersey pocket a couple of times and it never worked. The only thing that happened was it weighed down my jersey and got wet and ruined with sweat. I still need a baggie for the Razr that I carry on my rides in case of rain, but that's kind of irrelevant I guess. I had to get used to being a minimalist, as I used to carry around a metric ton of crap in my wallet. I actually love not having all of that bogging me down. My buddy John actually couldn't part with enough stuff to use a jimi, so he still carries his traditional wallet. As far as your son, he has good taste! Enjoy the jimi and use it in good riding and good health.