I like them because not only are they neater, but cooling a room can become a problem the deeper into a mountain you go. (I like to have my colonists live in hollowed out mountains)
The power is probably not as balanced as it could be, but you'll have to take that up with the developer of the addon. :)

As a general rule though, I have only used the original "vanilla" air con units to cool my walk in freezers, as they seem good enough most times.

Again though, like the little compact air cons, the walk in freezer units are great if you want to put in another freezer space but just don't have the room to put in a tunnel for the hot exhaust....or perhaps you don't want to supply tunnels to the outside world, because that's a weakness in your defences.
THAT is a very real danger and a reason to use them instead of the usual ones, I suppose.
Helps with defences. :)