Im the owner of 2 russian dwarf hamsters,
This was bought as a add one for my large rotastak system, it would be cruel to use it as a full hamster cage as its far too small even for a dwarf hamster.
It also would not be suited to a dwarf hamster the way its layed out on the picture as they cant climb verticle tubing, but you can change the way the tubing is attached by using the hole on the side rather than on top.
Also rotastaks are so hard to build you have to have alot of patience!
Its a excellent buy for what i bought it for, so as a extra to your existing cage i would recommend.