At only 22" wide, it's a really narrow cafe and it doesn't provide much floor space for running around.
If you already have two of these cages and you're interested in combining them,, I think it makes much more sense to create a wider cage by having them side-by-side. I don't see much value in stacking them and having a super tall cage with practically no floor space.
I 100% don't think it would be worth paying full price for two Rat Manors with the intention of combining them. There are definitely better cages on the market.
It's better to give rats horizontal space rather than vertical space. I would put them side by side if you already have them, but like Corbin said, it would be better for the rats to just buy a cage that's already bigger.