Finally got to go here recently and enjoyed my stay.
If you need to be at the frankfurt trade fair/congress (MESSE Frankfurt) then this is your hotel as it's literally across the street.
Weekday rates are high because of this, but good deals can be found on weekends
I was upgraded to a nice rennovated room on the 43rd floor with a pretty far reaching view facing southwards I think (not towards frankfurt skyline). The room had mini bar, walk-in shower, a desk, a small sofa/couch area with space for 2, a round table next to the sofa area, and quite large windows, one of which which you could even open very slightly for fresh air ! I did not expect that on the 43rd floor.
As mentioned above, the lounge is now on the ground floor and has no windows. However, it makes up for this by firstly being very large. I saw at least 20 tables and a few sofas with lots of free space for more tables if required. Secondly, it was the largest evening food selection I have seen in a bonvoy hotel lounge for a long time. At least 4 to 5 differerent warm items plus warm soup, salad bar, a few different desserts and various other nice things. I was impressed by the variety on offer.
Only complaint with this hotel was the elevators which takes ages to arrive when busy. Despite there being 4 elevators, one seemed to be out of order and the other 3 still had delays more than a few times.
As mentioned above tram numbers 16 and 17 stop directly in front of the hotel. Get out at the stop called "Ludwig-Erhard Anlage". This is much better than the metro as you do not have to use stairs/elevators.
The journey takes about 5 minutes and you can buy a reduced cost ticket called "kurzstrecke" which is for short journeys and only costs 1.85 euro each way.
If you really want to use the (u-bahn) metro, the closest station is "Festhalle/Messe" where line U4 passes through.