Does it save you time? Probably. I've taken a car service to my WDW resort, as well as the Mears shuttle, and DME. Never a cab though. For just about the same money, I can get a private car service.
With a car service, my times have been 45 mins with carry on bags only, and about 60 mins with checked bags. With DME, I've had times as short as 60 mins, but as long as close to 90. Most have been in the 70-75 min range. So, you need to decide if spending about $60 is worth 30 mins.