Hi Toppleover,
I prefer Futures personally and yes I have rolled the odd fin box. Usually when hitting dry reef.
I have also used FCS and am not a big fan. I've snapped FCS fins in a hard fast bottom turn

and when the board has washed up on the beach sideways

Both fin Systems have a great range of choice. I think the strength of the box comes down to how it was installed to a degree.
The new plus for FCS are better but the plugs aren't the problem IMHO, it's the fin base tabs.
DM