My opinion is that they can do more damage than good. In my opinion if you treat the battery correctly and put a charger on it a couple of times a year you will be better off.

I have a Schumacher 3 amp trickle charger on my marine battery and it destroyed the battery by overcharging it. It boiled the water out of it. The charger failed - it never shut off. They sent me a newer version under warranty and this unit maintains the voltage at a significantly lower level than the older one.

I personally would not be using a trickle charger on my vehicles.

If nothing else, they are an additional fire risk.