It's a particular pet-safe grade of mdf by the sound of it too. MDF tends to be heavier than wood but anything that size would be fairly heavy I guess. It looks nice on legs
I wouldn't have a problem with limited roof hanging toys in something that size - you can make up for it with adding platforms with toys on and could still have a hammock or sputnik or a tube tied to the roof if places carefully. I wish it said how big the slots were! You can assume they wouldn't be bigger then 1cm but it would be nice to know. Not sure how that would work for dwarf hammies.