I bought a refurbished 12 mini a couple of years ago from the UK Apple Store (also to replace a 1st gen. SE) and have been very happy with it. I've had no problems with battery life; unless I'm using the camera a lot, it easily lasts me at least a couple of days on a charge. I'm a very light phone user and not worried about always having the latest OS, which is just as well as it seems small phones are now a thing of the past, so this is going to have to last me for many years to come! I chose the 12 mini over a newer SE because of the better camera and greater useful screen area in a very compact design. Replacing my perfectly good original SE with basically the same thing but a bit bigger seemed rather pointless. I also prefer a square-edged iPhone to the slippery rounded edges of the current SE. I was a bit anxious moving from the home button to FaceID but very quickly found that to be a worthwhile upgrade too. Personally, as a price-conscious light user, not worried about the latest bells and whistles, I'd say go for it.