...fin ... like the DiveR's
On an entirely unrelated side note, I soo hate idjit webmonkeys who put shiny! audio meedja on their websh*te. Ever heard the phrase "workplace friendly"? DiveR products: get back to me when you get a clue.
Somewhat more related: I'm pretty sure freedive-length blades work much better with wide arc kick. There's of plenty of reasons to prefer shorter blades that don't. Regardless, you're still doing it straight leg, pointed toe: "untrained" people tend to not have enough stretch in the ankle to do that right; kick drills in swim fins or no fins will help with that.