Do not recommend. Hassle. The Uptown blue line is NOT hop on hop off. It’s only start & stop is at #16, in front of the Olive Garden at 42nd St & Broadway. It’s a 1 hour trip. Audio tour was good on this line.
The red downtown bus can be hopped on next door to above blue line from Olive Garden in front of the Knickerbocker Hotel (stop #16).
If you hop off red line to see a few sights, you may have to walk a long ways to hop back on a bus at different location, depending on where you walked. Not to mention waiting for a bus that may never come. This is what happened with me. Walked a mile to get to stop on red line, arriving at 5:30 pm but no more buses. The 2020 brochure needs to be improved/updated. The app was confusing. Could not figure out time of last bus at a stop. Buses were shown on the line but frozen in place. /Fortunately, the guys selling tours on the street were very helpful finding the start of the uptown route (stop #16) as brochure not clear. / The yellow, green, and purple lines were not working. /The most prevalent hop on hop off bus in Manhattan is currently the TopViewny.com bus, thus recommend TopView. The Grayline hop on hop off is not operating. Please know, if you buy the NY Sightseeing Pass (which I do not recommend), the Big Bus hop on hop off is good for only 1 day.