I've tried Magic Trackpad 2 on a mid-2010 iMac 27" and a late-2009 iMac 27". Both do not have BLuetooth 4, but the trackpad pairs and works fine with the latest MacOS versions.Does this work with mac pro 2009? or any mac computers older than 2012?
Also, for me the new Magic Keyboard is fantastic. I was very hesitant with the new keyboard on the MacBook 12" after first trying it in an Apple Store, but giving it a further chance I feel it is the best keyboard around. My typing accuracy and speed has certainly increased. I love that I can now experience the same improved typing on my desktop Mac.
So, from a usability perspective, both Trackpad and Keyboard are top notch. In practical use, I don't think the built-in batteries will pose a problem. My first AA battery-operated Apple keyboard was rendered useless after a couple of years due to leaking AAs ... so much for the superiority of replaceable batteries.