I've just fitted one of these PiperX kits to my ZR+120 too.
I've never before even been inclined to mod anything under the bonnet but was convinced this was be a synch. Also, I was given expert guidance. But it really is straight forward.
Word of warning: instructions that come with it are bollx, at least as far as ZR fitting is concerned.
Only problem I had was that the black bracket did not fit over the existing bolt securing the rear half of the air filter casing to the battery surround. Had to trim it down a bit. Other than that 10 mins max I guess.
No ducting required. Lower half of air filter casing remains as it was. PiperX just sits on top.
Mine might be a bit high. Will get some pics for next week and see what you think.
Oh and price is £69.99 but then there's VAT and £5 P&P. Comes to just short of £80 in total.
And on the website, it specifically fails to mention the ZR105. Don't know if this is a mistake or whether it doesn't actually fit the 105. You'd need to check that one if you fall into that category.
As for performance, again it maybe psychological but the first 3 or 4 standing starts having fitted it I wheel spun and I wasn't trying to!
Also, I reckon deep roar noticeable from about 2,500rpm onwards. More you floor it the bigger it gets. Took 2 mates out in my Zed last night. One was convinced I had problem with the exhaust (he's a sensible Corsa driver) and other reckoned it was well minted.
F