I fly two Mondays a month at ~7 AM, have never been remotely close to missing my flight with a 4:45 AM scheduled Uber + TSA Pre. I used to schedule a cab but the company I used upped the cost to $80 whereas Uber is typically 40-50 bucks. If you're worried, call a reliable cab company, but coming from Waltham and Watertown I've never had an issue with the scheduled Uber.

With that being said, I hate that Uber is so much cheaper because they just fuck over the drivers and I'd much rather pay a cab driver, but the pricing is just not competitive at all in my areas.