This was the first cage I bought, the day I bought my first girl. I still use it despite having the monstrous DCN in my basement. The Rat Manor is really the home for my rats, while DCN is "vacation home" for daytime when upper level of my house is too warm. It is small by comparison to DCN, and not very solidly built, but it does the job very well. It is a home for two girls (one skiny, one fat, lol), and a big boy. It doesn't seem like they are cramped. I usually put 2 hammocks and a tissue box. But you can fit 3 hammocks if you want. Nevertheless, the ratties most often stack one on top another in just one hammock.
The one big con of this cage is that after a few months the bottom pan started to rust in corners.
I think that would be an ok starter cage for two rats if you free-range a lot. Young rats are usually quite active and rat manor doesn't have a lot floor space to play and run around. But yeah if you are not planning on getting more rats and you can offer your ratties a place to run and play daily, it's ok.
I would say that is would fit two males or three females, but that is packed to the limit. I would say two of either gender is as many as I would put in. It works quite nicely for my two females, I took out all the levels and replaced them with hammocks. Although the doors are a bit small.