We have had pretty good results, except for our departure last year. The bus was late (actually, never arrived, instead, a taxi arrived on Mears' behalf about 1/2 hour late). We were concerned that all of our luggage wouldn't fit (it did!) so it all worked out well in the end. (i.e. with the taxi solely ours, no stops along the way to pick up others, and we made the flight with much time to spare).
Otherwise, every other instance (and we have used Mears for round trips to and from Disney resorts for 6 years, all were fine). We did stop at other resorts along the way, but the excitement of arriving overcame any slight delay in ACTUALLY arriving.
BTW, we are doing the towncar this year (maybe the stretch limo) just to surprise our children. (we're saving with annual passholder rates and two trips in one year, so we thought we would splurge).
So long as you don't mind seeing other resorts or being "not the first" drop off, Mears is fine.
Have fun!