Vicenarian, I'm going to go out on a limb here and guess that you really like the Kanguru drive. lol
Seriously, I would consider this (or something like it) except that I like a bit more breathing room. I bring a 500GB drive in a Rocketfish usb/esata enclosure with me instead of a thumb drive. Allows me to carry ISOs of XP, Vista, and Win7 for OS reinstalls if the client has lost their media, plus UBCD, BartPE, a few different malware/virus scanners, and other assorted utilities while still having plenty of room to backup client data right on the spot if I need to do a format/reinstall.
I know this may seem excessive, but most of my clients are older retired people who don't mind one bit if I remain onsite for a prolonged period, but don't like having their computers taken offsite unless absolutely necessary. I think a lot of them just enjoy having the company for a while.
I'm just getting started, so I can't afford to do a proper hardware write blocker solution, but would love it if I could find an inexpensive way of getting at least some protection without sacrificing drive capacity.