You are most welcome to dyno test the O2 mod if you want to, there has been a few guys that have done just that by testing the mod on a dyno & with data loggers & are happy it works. The proof comes when you ride your bike after the mod has been fitted, it will work or it won't you will be the judge of that.
Ask your dyno man to try & build a fuel map without the O2 mod, I bet you won't be able to map the fueling without the O2 mod below 4000rpm. If he wants to test the mod on the dyno I hope he is not going to charge you, he will need to do a before & after dyno run to do a fare comparison.
If you are worried about fitting the mod yourself I can always talk you through the fitment if you want, I am alway here to help out.
I would not publicly sell these mods in an open forum if they did not work. Have a read on this thread about riders reviews.
http://www.xt660.com/showthread.php?t=14746&page=8