Hey,
So bought a cheap used surfboard and one pair of FCS fin boxes became loose on my first session.
I watched this vid and have prepped my board accordingly:
Salty,
If the board was cheap you'll send more time and money with a repair than to just replace it plus the extra weight and the risk of another plug out...
Early FCS was not made to take the stresses when used as a kite board.
Maybe do the maths before you start the exercise....
Unless your wanting to teach yourself board building / repair then go for it....
If the ocean and earth kit is ok, it'll be a $30 repair. My time is not important. a repair from a surfboard shop is $90, the board cost me $150.
The product that you have chosen should be fine. Your success is going to be determined by how well you prepare the damaged area. Make sure you dry out the damaged area really well and that there are no traces of salt. Sand the glass around the repair area well.
Can't see the vid as I'm at work. The O&E kit you show should be fine the only other thing you may need is some milled glass but you only need that if you are actually taking the plug out. If the plug is in place and you're just going to resecure you'll be fine without it.
hmmm, if that's where you are at then if you got some rovings and some sharp scissors you can probably roll your own milled glass by taking very fine cuts at the rovings. The job can be done without the milled glass but I wouldn't recommend it. If they haven't bored the hole twith the hole saw through to the deck I'd do that now as it makes a huge difference.
Mate I would definitely suggest going to the fibre-glass shop and getting some polyester lam (if it's polyester board). This will cost you less than 30 dollars for a litre of the stuff. Make sure you get a little bottle of catalyst to.
Q-cell will not increase strength, it is used for filling spaces and making it easier to sand. What you want is Cabosil, this stuff dries really hard and does add strength to whatever you do. Only down side is it is tuff to sand back, make sure you get onto it before it dries 100%.
I would suggest putting a layer of cloth in the hole (like you were making a pie with dough in a tin) and then putting the plug in after. Once you have sanded back everything flush, cap the plug with a small square of glass and it will add a ton of strength.
That's why you put the resin in the hole first then push the cloth in with the plug. I've done this many times before and never had one break back out again. You are free to do as you like though! 
There is no strength in resin, you have to use fibre glass with it. What I have done in the past is cut up a bit of fibre glass in 1cm pieces and played that in the hole before putting the fin plug in, also make sure the resin connects with the top deck, you can use a drill bit and make a number ofholes that bottom out on the top deck ( by hand).
Alternatively use epoxy resin rather than poly - its stronger.
Also you can glass over the plug, just fill the slot and the grub screw hole with some play dough and glass over but roughen up the plug to create a key for bonding.
I have repaired a number of fins like that and the boards a still going strong after 1 year and 3 years use.
Cheers
Rich
May I mention, just make sure you never use Polyester resin on an Epoxy board. You can use Epoxy on a Polyester but never the other way!
I know this might be common sense for most but just incase you didn't know 
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Did another quick fix last night. Pulled out 2 old broken plugs and put in two recycled plugs from an old board. Did the pie in the hole trick and mixed in a bit of Cabosil for good measure. Got up this morning sanded it back and went for a surf, all good! . Saved myself between 50 and 100 bucks to.
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Yea but the one does not bond very well to the other, I can't remember but I think poly does not stick well to epoxy - I suppose either way the bond will not be so great.
Another option for a quick fix is to use the Selley's type of epoxy, usually it is very strong without fibre glass so it is ideal when away from home.
Repair dings with it too, spread it in the hole, put a bit of spit on your finger and shape it, use a different finger everytime as it taste like sh!t and can't be good for you - this all sounds a bit dodge.
At the end of the day any fix will be only as strong as the material you are bonding too therefore balsa wood is ideal to increasing the strength around a fin.
Cheers
Rich
Epoxy doesn't stick quite as well to Poly if you were laminating one layer of cloth after an other, but it will stick about equally as well for a repair job, and an Epoxy fix should be slightly stronger. Epoxy job will also go brown far quicker than the rest of the board if it's poly (if you care).
But as Rich points out your job is only as strong as the weakest link! haha.
