As per Dr Farkoff,
And - Fekking noisy. Fitted one, took it off a few days later. If you are heavy handed at lower speeds and open the throttle widish/wide, it sounds like there is some kind of drift competition going on and peeps start looking round in alarm......And also it messes a bit with the fuelling and (at least on my G/S) made it somewhat lean with a bit of a more pronounced flat spot at 3-4k ish, right where you dont want it for real world riding. YMMV or course...
The existing airbox with its different sized snorkels actually does a decent enough job, and would you really notice the extra 2 bhp Richard claims? (I dont doubt his claims BTW, just saying) presumably its at higher revs, where a standard road going airhead is not at its most "mechanically comfortable"......If you are racing your bike and in conjunction with other suitable mods, go for it, otherwise........
BTW if you must have an airbox/filter mod, you can just get a K&N that fits in the standard box, and IIRC K&N make similar claims about extra power, with the bonus that you never have to buy another airfilter again. I have one and its fine, cant say the extra claimed power was noticeable (no surprise there) but I dont have to throw filters away anymore, just occasionally clean and relube and its stock OEM looking.