Pros:
They survive high mite levels.
Cons:
They head butt and pull hair a lot. They are runny and prone to propolize (but that might be a pro?).
The fact that they are frugal could be a pro, but this also means they overwinter on a small cluster and build up later, and if you want to pollinate almonds that's a con, if you want to make honey, it's neither, it just is. They make up for the buildup by exploding later. This also could be a pro or a con, as an explosive buildup can easily lead to swarming but it also means they have a population to haul in the flow if you avoid the swarming.