"I confess I haven't actually had this recipe per se BUT I have made several key lime pies with different recipe variations similar to this and will have to try this one as well.

In advising those who want to try it with fresh key lime juice: halve and juice the limes using a fork or citrus reamer (Ikea sells a $5 reaming juicer - Spritta- with dish that allows seeds to be separated during the juicing process. It has two size reams so it works well for all citrus juicing).
Do not use a press or squeeze/pulverize the peel. The pithe (white part) carries a strong bitter flavor that is way too easy to extract. If using zest use only the green part of the peel.