Hi - My understanding is as follows:
1) using the form on the back sells shares within the DRIP at stock market rates. You can't sell shares in certificate form.
2) the buy back allows you to sell shares in certificate form and in the DRIP. The buy back is also calculated based on the Net Asset Value / share. According to FAP's website, there is an approx. $0.50 CAD premium on the NAV vs the market price. The buy back is not a market transaction so FAP can pay any price they set.
The risks are that, in the 4-6 weeks between electing to use the buyback offer and the transaction taking place, the market price rises higher than the NAV/Share. I don't think this is particularly likely but it could happen. A second risk is if the NAV/share drops precipitously in the same time frame. There would have to be a massive write-down or default of some asset for this to happen. I don't think that's likely.
If this is incorrect, please jump-in!