A little late maybe to chime in here. First, Ultra... surprised to see you talking Milwaukee and not Stihl knowing you are on that bandwagon as I am.
I am extremely happy with my growing fleet of Stihl battery line of tools. I went with the Stihl AP battery line of tools but for most with occasional use on small properties would do well with the less expensive/lighter weight AK line.
That said, I think it makes good sense to try to standardize on a brand so your battery or batteries are kept at a minimum. If you are already committed to a particular brand with more than one tool, probably should look hard at what direction you want to go long term. Everything is going to battery.