We have been testing Seymore Butt's official site
http://www.seymorebutts.com from some of our own sites and the conversion and retention rations are crazy. It's a free 3-day that converts to $34.95 and were averaging about $27 per signup (only been testing for 3 months).
Even the chargeback's that you would normally expect with a cross sale are MUCH lower that we though, and to be honest we were worried about this at first.
So if your using Jettis for your billing, it's about a 5 minute process to set this up, it's definitely worth a try.
Hit me up on ICQ, if you need more details.