I had a bad experience with Paxeos. I had to take a flight at 630 AM last week (Feb 12) from Managua airport and booked the first shuttle out from Granada at 4:00 AM. I reserved my spot 3 days in advance and was asked to come to the office at 3:45 AM in the morning. To be safe I showed up at 3:40 AM. I waited until 4:20 AM and no shuttle showed up. Thankfully cabs were still running in the streets since it was early Saturday (late friday night trips for some). I just barely made it for my flight else would have been a disaster.
I'd like to highlight that when I made the booking I was kind of paranoid given the awkward timing of my flight and the possibility of not having other options at 4 AM, so when they took down my info I made sure it was all clearly written down i.e. I would be outside their office at 3:45 AM etc....and that it was a confirmed seat and that the driver stops by the office etc. Disappointing. Given the shuttle costs $18 and you can get a taxi for yourself $30 (quite easily without much bargaining), its really worth it to take a cab to MGA. If you are more than 1 person, its a no-brainer, take a taxi and they are quite fast. And in my opinion, even if you are 1 person, suck up the $12 and take a cab. Its worth it.