I experienced the new shuttle routes for the first time yesterday. Terminal B to the Blue Line in the morning and the reverse in the late afternoon. The morning trip obviously was fine as the Blue Line was the first stop after I boarded at B. But I almost missed my flight on the way back, as the rental car stop after the T station added a good 15 minutes to the trip. There were multiple buses backed up at the rental car center.
I hope they have a plan to have dedicated routes to serve just the rental car center, because the current routes are bad both for T passengers and car renters.