I use them all the time on vehicles that see very little driving time and see very few actually fail with maybe 50% of my clients using battery tenders. Years ago we spoke to Optima and they recommended the Yellow top over the Red top for vehicles that see limited driving. They claimed that the yellow top had a faster recharge rate than the Red tops.
I've gotten in the habit of providing all of my clients that don't already have tenders with the Optima Battery 1200 charger. Gives them a good charger without the forementioned having to rig up extra batteries to charge, plus it has a tender feature.
http://www.optimabatteries.com/us/en/products/charger/
For you guys that are going through batteries I would definitely check for voltage draws.