He's correct. I have personally tried it on the nine and the nineMX and it dosent fit.
If you're hellbent on getting wisdoms, and dont wanna buy a new helmet, but the strap for 15 bucks, it helps but still, there are much better fits.
As for if you don't mind getting a new helmet too, the Bad Lt. works. I skied Bad Lt.+ Widsoms for the second half of the season and it worked sick. Remember tho, strap under the helmet, not over it.