Once you have the tree house, you won't need the plastic top cover. There is usually a small bit of difficulty putting the Tree House into its place, because the ladder is too long and tends to stay vertical (thanks to gravity). You must remove the lid and shift the ladder such that it is sloping and only then will the Tree House fit snugly.
Not all hamsters are smart enough to climb the ladder. Some prefer climbing up the chute (and it is really slippery for the younger ones). Naughty hamsters will keep you awake when they start biting the lid (which also tends to shake). The top cover of the Tree House will snap shut, though with much less force as compared with the Solarium.
Hamster satisfaction: 
Maintainability:
Owner satisfaction:
