After foolishly buying a Savic Spelos for my two hamsters when I intended them to live together, I found out they were boy/girl and had to be separated. I didn't like the Spelos at all, so returned it and bought two Ferplast Mini Dunas, instead.
They've been in them a week now and seem pretty content. With the level, there's plenty of space to run around (although they also take to hiding under the level), and as there's only one in each there's enough room for a regular Silent Spinner and a few other items. I use the food bowls that came with the cages as sand baths - I just scatter the food among the sawdust and they seem to like scrabbling for it.
One challenge has been getting water bottles for the cages. I didn't like the sippy bottles that come with them, but am not a fan of water bowls either. Right now I'm using test-tube type bottles that attach via suckers inside the cage, but I'm not convinced the water always flows properly in them. At this rate I might give the sippys another go.
But overall I like these cages and think they are a good size for up to two Robos.