I have a CTEK MXS 5.0 hooked up almost continuously to my Jaguar for the last 3 years. It has an AGM battery and those cars are notorious for doing odd things when the battery is not at full charge or starts to degrade over time. The car is not a daily driver so keeping the electrical system in top condition is essential.
I also used it to put a full charge on a brand new AGM battery that I bought for my Mazda CX 5 before installing it and if the 5 year old battery in my Generac generator starts to go out I'll try it to recondition the battery before I spend the money on a replacement.
Sure the CTEK units aren't cheap. They currently run about $100. But the difference between a CTEK and a lot of the others is what a couple or three combo meals at McDonalds cost these days. I'd rather spend the money on quality tools than on fast food.