I use Logan Park 'n Go all the time, as I travel a lot for work. It is not operated by Logan, but rather it is a private company. I have found it to be safe, convenient and quicker and easier than parking in the Central Garage at the airport.
Their are good directions to the location on their web site.
It is about a 10 minute ride from their location to the airport terminals, maybe a bit more if you are the last stop.
We will be using them for our October trip, as it is cheaper than any other option. We are flying on Song in October out of Terminal A, so we will be the first stop.
I was there last week about 10 PM, returning from a trip. It is well lit, they drop you right at your car (When you park they give you a slip of paper with the exact parking spot location noted. We you get on the shuttle on your return, you give this slip to the driver and he takes you right to your car.) Their was a security guard there too.
I have never waited more than 10 minutes for the shuttle on my return to the airport.
I am curious - does anyone know the name of the park and fly hotels? TIA