Offsite shuttles can be very unreliable & inconvenient. I stayed offsite once (NEVER AGAIN!) and that hotel ran a shuttle 3 times a day to Epcot only. You had to sign up for the shuttle the day before & it was first come, first served. I never got the shuttle time I wanted because I was at the parks at the time they opened up the sign-ups. The shuttle was also shared with 4 other local hotels, so the bus was always crowded. It took 90 min. to get to any other park (it only dropped off & picked up at Epcot, so I had to transfer there). It picked up at 10:30pm WAY out in the offsite shuttle parking lots at Epcot which was a hike at the end of a long day! The shuttle also was always running about 15-20 min. late.
I'm sure some offsite hotels have a better shuttle service, but my experience has scared me away for good! Onsite Disney all the way!