I have installed a number of these panel protectors and the instructions always say it must be protected by a breaker.
The ones FPL put in the meter base are utility equipment, covered by the NESC but I bet there is some kind of overcurrent protection built into them.
My lightning protection scheme is basically a couple panel protectors, one in the main panel in the garage, one on the house sub panel and point of use protectors on critical equipment.
So far so good and I have had lots of close in strikes including two directly into my weather station mast.
<firmly knocking on wood>