I spent lots of money (£313) and bought a device which is a high power charger, a smart reconditioner/tender/maintainer and a 40A battery support Unit in one. I've used all these modes now and I'm very happy with the product:

 

I've had some close calls with lesser brands that I've already posted about on this forum including one explosion with minor damage to the car. I figure if I'm going to leave an expensive car unattended and plugged into an outlet in an even more expensive building, that's not where I want to save money. And yes, it can be very frustrating when the CTEK detects some sort of fault and refuses to charge, I've been through that too, but, that's far better than burning your house down. I wouldn't use any battery maintainers at all but if you are going to have more cars than you can drive frequently and far enough to maintain the batteries naturally, then its kind of necessary.

Couple years ago I won an Everstart battery maintainer as a door prize at a car show. I think its an exclusive Walmart brand. I haven't even opened the box. Don't know what to do with it. I've thought about giving it away or donating it back to be a door prize again, but I'd hate if it damaged somebody's classic car or worse. It'd probably be perfectly fine, but after my own negative experiences, I'm a bit gun-shy of the cheapest units on the market.