That is the most inexpensive boost controller I've ever seen. Basic principle behind it is good, too. Find the right spring for it and it should work fine.

Here's plans for one like you'll see on Ebay. More complicated, more expensive. If you add a 5/16 ball bearing (depending on how big you tap the screw fitting out to, mine was 5/16") to the other side, it makes it overboost-resistant- if the screw falls out, it goes to minimum boost.
http://www.geocities.com/chmwatson/FAQs/mbc.html