Future fins have no gap between the fin and the board, just like glassed on fins, but you can change fins for different conditions. They wont pop out of your board like a FCS set up can do in heavy situations. Glassed on fins are really cool, but if you ding one its a problem fixing it, where a fin system you can replace it. One time I remember having these hi tech carbon future fins in my backpack, and I was too lazy to change them out with the plastic ones the board came with. One session it was firing, and my board wasn't making sections, and the fins were humming, so I finally changed fins. Lo and behold, I was flying around sections, getting into pockets and shredding and going really fast, and I laughed my ass off at my own ignorance. Do not be tricked into thinking you have the right fins for your board until you try a few combos. On big days, I have a 6'6" Orion swallowtail that is too loose for a big drop when I use the G 3s or even G 5s. So I plug in my old Sunny Garcias and it holds big bottom turns. When it gets smaller, like waist to chest, I can put a small trailer fin in the back and throw tail. so keep you options open and get a removable fin system. I recommend Future shapes cause they are almost like glass ons, but more fun.
I don't think it's worth it. You might feel a little difference, but the convenience of switching fins and removing for travel outweighs the performance... If that becomes your "go to" board it will be a pain in the ass when you want to travel with it.
I had a board made with glass ons of the fins I prefer and I feel no difference between that board and the one I have with FCS.
Glass-on fins have the stiffest base possible (they're part of the board) and transfer force most efficiently. Some finbox systems have stiffer bases than others but chances are you wouldn't feel the difference between any fin system vs. glass-ons
Glass ons look cooler, but it sure sucks to have to pay for board repair in the event you snap a fin off. Easier to just pull the broken off nubs out of the fin box and to slide in another fin. I like the option to switch fins personally. I have had a lot of success and fun trying different fins from the ones that came standard on a number of my boards. Like one of the above said, when its smaller surf, having a small trailer, or trailers (quad) will loosen up the board and make it super fun. If you have a few boards already, screw it, get some glass ons. If you're getting a bonzer, I assume you already have some standard boards in your quiver.