I held off for a long time before going to fiberglass blades in stiff Omer footpockets, but really like them. I have a pair of modified Picasso Black Teams (thinner and shorter) and when I went to SpecialFins medium Blue Water Specials I really did get to the bottom at 50 ft for spearfishing faster and easier. One day I tried both. There was just no comparison.
The other part of it is the softer medium blades worked a lot better than stiffer blades for me. I can't separate effect of the softer blades from the fiberglass. I don't know any divers who have gone back to plastic after using fiberglass or carbon fiber, so that may be a pretty good recommendation.
have you read the stuff on Deeperblue about blade performance? Here is one review of the blades.
Plastic vs Fiber Fins: Another View by Sven Anderson on DeeperBlue.net - Fanatical About FreeDiving, Scuba Diving, Spearfishing & Technical Diving