We offer a variety of "freedive" fins. Your buddy's opinion about the benefit of freedive fins is shared by a large majority of scuba spearos, many professional scuba guides and an overwhelming majority of freedivers and freedive hunters.
As to which fins to buy for scuba, a lot depends on your budget. Our most expensive fins are carbon fiber blades, then going to less expensive options: composite carbon/fiberglass then fiberglass then composite (plastic) blades then fixed blade plastic fins (meaning the blades are fixed in the pocket).
In all honesty, the benefit of the most expensive carbon fiber blades is not huge for scuba divers - because they are pushing so much gear around. In addition, those are expensive blades to have on the boat where people are dropping tanks and other heavy things.
Generally we see suba divers choose fiberglass or plastic blades. You mentions the Cressi gara plastic fins. We have a very similar fin:
View attachment 400033
Freedive Hunter Freediving Fins | MAKO Spearguns
However, because we sell direct to the consumer without the retail store mark up, these quality fins are much less than you will likely find the Cress 3000 fins. They are $68 on our website.
If you want replaceable blades then we recommend the competition freedive fins.
And if you want to spend around $200, we offer our fiberglass blades in both a soft and medium blade hardness. For people under 200 lbs we recommend the soft blades for extended swimming.