Yeah, I find it a little odd that Paul condones shifting with your finger or foot.. From the website:

"One of the coolest things about the Melvin is that it allows two front chain rings to be used (of course this is no longer a single speed, sob, but can be very handy for loaded commuting) Because we use two pulleys, two chain rings with a maximum difference of twenty teeth can be used up front. With a little practice, a deft finger and a delicate heel make a fine front derailleur."

I don't know about you, but I don't like getting crap all over my hands/feet and riding.. My last application of white bar tape was totally slaughtered by having to make an emergency chain-slop fix on my geared bike, with no place to wipe that nasty black schiesse but my new jeans or my new shirt. Bummer.