Somehow you didn't get the correct link for the charger. Is this the one you bought?
What amperage does it charge at?
Something to keep in mind is that besides worrying about overcharging (which this charger indicates it is a float charger) is using too high an amp rate on the "sealed" gel cell batteries typically used for starter boxes. If charged too fast they want to build internal pressure and vent. I bought a Hangar 9 charger from the lhs that specializes in planes, it was $10 and is specifically intended for gel cell batteries. It charges at 600mah, and my understanding is that you really don't want anything over 1 amp (1000mah).