I have one recurve that is not "FF Rated". Even with a well-made Flemish B50 string, it just lacked "umph", if you know what I mean. I tried a couple different strings but the bow just wasn't a performer like I thought it should have been. So it hung on the rack and it didn't get shot very much. Then after conversing with a couple fellas about modern material strings on non-FF rated bows, I put a 18 strand Fast Flight Plus Flemish twist string on it, set it up and gave it a new whirl. I figured I wasn't shooting it much anyhow so if something broke, well, at least it broke being shot. The change in that bow with the FF Plus string was amazing. The new modern material string really woke up a sleeping dog. The bow suddenly was much more pleasurable to shoot, and the cast/trajectory (speed) was MUCH better. Not sure how much better as in fps (no chrono) but the cast/trajectory really improved and the "feel" of the bow being shot really improved. So much so that I now shoot that bow more than any of the rest of my bows. The bow has beefy limbs and tips and upon inspections, see no damage at all, so far, from using the modern string material string on it. Maybe the 18 strand thickness helps ease the load on the tips? I don't know for sure. It might crack or break tomorrow....but could also from using a B50 string. In any event, the gains from using the FF Plus string over the B50 outweigh the risks, for me and for this bow. It went from being on the sideline to now being shot almost daily. Time will tell I suppose if the FF Plus string damages it or not. To this point, after a month of shooting, all is well.