So yeah I think my biggest concern about this... I have a mechanic. But even if I didn't... I would want a mechanic. I don't want some random guy showing up each time. This isn't like Uber, it's more like a dentist... I guess some people probably don't request the same hygienist each time... but I some jobs I want done by someone I have a relationship with. I want to deal with the same person on a regular basis, know he does a good job, trust him, and not leave it to chance each time I need my car serviced. Maybe it's different for people in bigger cities...
If you think about how their service started--as a tire replacement service--I don't think it's as concerning. If I wanted my tires changed or rotated I don't care who does it (I always took my bike to the CycleGear but that's just because they always had good rates for tires). But once something big happens to your vehicle I'm with you and can't imagine calling over a random mechanic (nor do I think they can do a sufficient job repairing it in a driveway).