...except butanol is nowhere near as easy to produce as ethanol.. You gotta make ethanol on the way to getting to butanol.
Looks attractive, and is, on the small scale, but not scaleable the way ethanol already is. It will surely be used in some quantity, but it seems that ethanol is a better fit overall- most of the same benefits with an easier production process and existing scale.
here's their booster website:
http://www.butanol.com/