We used the Go-Go Babyz Travelmate that you mentioned, and it did provide a nice rolling seat for our toddler to use as we moved through the airports. However, our convertible carseat, the Britax Marathon, proved to be too big to fit comfortably in the airplane seat. Our daughter's feet would have been kicking the person in front of her for the whole flight, and we just could not do that to someone. We ended up just having the flight attendant check the travelmate and car seat for us, and it was waiting at the gate when we arrived at our destination. Because she was under two at the time, she rode in her own seat on the way out and on one of our laps on the way home. She was fine. It was nice to have our own car seat with us at our destination, but I am not sure I would do it again. So, yes, the Travelmate works, but you need to figure out how badly you need your own car seat at your destination.
In addition, I have had to change a diaper on the plane, and it is quite difficult. Both flights we were on were on older planes that did not have changing stations. In fact, I was told by flight crews that only a very small number of new planes were being equipped with these. So, I had to just lay her across the closed toilet lid (on her changing pad, of course) in the tiny bathroom. As fate would have it, I had to change a #2 diaper both coming and going, and the situation was comical only in retrospect. It can be done, though, even with a very tall 20-month-old. Just make sure you bring an extra outift for baby, and maybe even an extra shirt for yourself.
Have a happy trip.