FCS2 allow for a little bit more fore/aft adjustment,
if you think you want to play with placement more.
I’ve tried to adjust fins up and back with Fusions and there really isn’t much wiggle room and it’s hard to get the fins to stay put since you get a little indent on the tabs that the grub want to engage. Do you find FCS2 to be better on the adjustablity then when using 2 tab fins in terms of staying in place?
If its a standard FCS2 install with the jig cross hairs placed on the shapers dots, then the movement of twin tabs is entirely in the forward direction i.e no aft adjustment. The movement is quite a lot though - about 1 cm. So good for loosening up your board, but not so good if you want to stiffen up the turning/drive.
If you are doing the install yourself with the intention of only using twin tabs, you can of course place the shapers dot slightly more rearward than your target position to give you that aft adjustment, but this would rule out putting in FCS II non adjustable fins on that position.
I know exactly what you mean about a fin only wanting to sit in one place in the fusion box despite the adjustment room provided. For fine forward adjustment of twin tabs in FCS2 similar problem. The screw will want to sit in the indent. For more substantial movement like 1/4" then it will go past the indent and not have that problem. Both situations could be fixed by elongating the dent with a Dremel tool or something, but that's a bit of trouble if you don't have such a tool.
FCS 2 is a much better box than fusion. The plastic fin tab housing is encapsulated in a polyurethane foam body which doesn't need wiping with acetone and should provide a more forgiving transition to the softer blank foam. The flange is perforated to give a good bond with the glass lam. I bought the install jig and kit (comes complete with the special router bit) and it is about $100 cheaper than the Future install kit. This was my main reason for choosing that over Future for self builds. I did the first install with the help of industry pro Josh Dowling who is a Gearbox fan. It was his first experience with FCS II and his comment at the end of the process was "easiest install ever".