In short, great guides, nice employees, a fun way to see the city - 1 or 2 days max to get a lay of the land and help you figure out what you want to come back and see, drop a pin so your not lost on the way back to your bus stop - Map from Big bus and app basically worthless.
Due to weather we were only able to use the downtown loop. The tour is very informative and would be a great "first day" active for a first time visit. We rode with several different guides (as we did hop on and hop off several times) The guides had great stories and background on the many remarkable areas of NYC. The loop takes you through many stops on the " east side" but after leaving "Battery Park" area the bus turns into a express up the westside and has no stops. The map shows a stop on 42nd Street (Port Authority bus station) but that stop does not exist. Speaking of the map or the app, it is quite worthless with the only bright spot being the app does show where the buses are and can help you see when the next bus will be at the stop you are at.
I would recommend "dropping a pin" with your phone when you get off the bus to help you get back to the bus stop after exploring the area you hop off. the bus stops are marked but you have to know what you are looking for to find the signs.
We visited in January and yes I knew it was going to be winter in NYC. With that out of the way I would recommend this tour but understand that much of the fun of the bus tour is being on top of the bus to enjoy the great view. In January with howling winds, snow and rain it is not as enjoyable.