That type of design with "vents" near the footpockets has been used quite a bit in Bi-fins. Started at least 30 years back with the original "jet fins" and is even used with some of the newish hybrid Jet fin / split fin types as well as other wierd designs. If my memory serves me correct there was a long bladed freediving fin with holes like that used in the "The Big Blue" movie.
Good or bad, I don't know. My thinking is that the part of the blade nearest the footpocket doesn't provide much thrust so perhaps the holes reduce the resistance but not reducing the overall thrust as much. It would effect the flow dynamics a lot, I'm not the expert on that.
I would be a bit worried if it makes the fin weaker. If after paying 400 - 500 Euro for fin and delivery, months of waiting... A broken fin would cause some pretty severe hair loss
