Change was made in sheffield. Previous versions of the rules specifically mentioned fiberglass as not appropriate. Looks ok for Aquachallenge.

11.3.1 Each player shall be equipped with a mask, which must have safety glass or other safety material fitted; a non-metal, pliable snorkel; a pair of conventional underwater hockey fins (made of non-dangerous, pliable, synthetic material) which is approved by the World AquaChallenge Association; a mouth protector approved by the World AquaChallenge


Besides Duck, there are guys on our team... or trying for the team, who are kicking quattros and need different fins. These look like the only good option for some of these guys.
Also not that i keep up with UWrugby but they've been using these for a couple years now and don't know of any safety issues that cropped up.