You don't say anything about the kinds of lawns you are cutting, size, and terrain. If you are working small properties, you may not gain much. If large properties (most likely, with a 52" mower), then you will see significant improvements in production.
I've had a one wheel, a ProSlide, and a two wheeled model. I used the one wheel model, until I got tired of either: (1) the mark down the middle, or (2) setting it aside and walking because I didn't want to mark up the lawn with the one wheel.
I got a ProSlide, and quickly learned my mower was too small to handle (36" Exmark, hydro). The idea is fine, but it takes some time to learn to use properly.
I replace with a BullRider, two wheel, convertible. I intended to use in caster mode, but again, my mower was too small. I used in trailer mode for a few years. It works fine, but for larger properties. For small properties, I set it aside.
I worked eight properties yesterday, and left the sulky at home. Just too much bother to manage. I don't mind walking, and can be quicker in many places without the sulky. At this stage in the season, I don't mind walking the 10 miles. Also, the wheels on the two wheel sulky leave harsh marks, much more than the drive wheels of the mower. They trail behind, but the difference is marked.
Three years ago, I bought a JD 717A Ztrak, so use the 48" ZTR on the larger properties. I could have used my ZTR on seven of the eight yesterday, but decided to take out the w/b anyway. Walking is good exercise.
If you were close, I would give both to you, ... just pick them up. Anybody else?