Something that just occurred to me about why some people say they "overkick" the fins and do not get good propulsion, is that they may buy smaller sizes that have smaller blades, yet they have strong legs (JohnnyC's comment about selling size L Pros). Force Fins tend to have foot pockets that can accommodate a variety of foot sizes depending upon the boots used. The blades on the smaller sizes also tend to be thinner, therefore they have more flex and therefore more "give" when kicked hard.
I early on figured out that if I used a size L, I would easily overkick them. Therefore I learned that I needed to buy a larger size and adjust to fit the foot pocket by the use of comfort inserts and the proper boots. I wear a size 10.5 shoe but I use size XXL Force Fins because they have a larger, thicker blade that fits my kick. My wife, 5'3", 125# can overkick size L in Pros but found that size L in Tan Delta worked fine or she needs to go to a size XL to get better performance (except she finds them too stiff in Tan Delta).
The other thing I have seen happen is people buy used "Force Fins" not realizing that they purchased Float Tube FFs - that are made with a softer urethane and smaller blade, so you can just sort of flick your ankles/lower leg to get movement. If you try and use them for Scuba or even snorkeling, they sadly disappoint.
I know that this takes more "thinking" to figure out the optimal fin style, material and size to find the optimal fin for your diving but it is not much different than deciding that you need 3 types of fins for the different types of dives you do. I only need one fin (Hockeys) for diving in the Quarry (5+5 mil wet), cool sub-tropical (3 mil wet), full tropical (84 deg+) or snorkeling. Yes, I do like to use my RIPs for playing in the surf and/or snorkeling, if I am on a non-dive trip (cruises) where saving some weight/space is required.
YMMV