Yeah, it makes sense to get the tools that use the same batteries as what you already have, if you have some battery-electric tools already.
My stuff is all Toro 60v stuff. At the time I bought into their ecosystem, there were fewer options available, but it's all worked well for me.
Greenworks seems like a pretty popular brand - even Costco sells them, and they tend not to sell things for very long if their customers aren't happy with them. That, combined with the generally positive reviews, would make me lean towards that brand. If you can afford it I'd stick with the 80v stuff though. (It's more expensive but it looks like the batteries and motors are beefier.)
IME, if you have a couple extension cords, a plug-in electric tool is usually more power for the money. It probably isn't a big deal for string trimmers, but most battery operated tools are limited to about 1hp (based on battery amperage and discharge specs) and a 120v household outlet can easily provide about 2hp of power, assuming the tool has a motor rated for it.