As others have said, it could be more of a preference thing to eliminate line-slip, but I tend to look at the other attributes that I found in testing. You see before r-bend frames, there was only traditional looped/twisted eye spinnerbaits, about 5-10 years ago, some southern luremakers & tournament fishermen found that r-bend frames would actually self-correct the bait on freefall on any cast, this is especially important when finesse fishing for bass because this actually prevents line-tangles/foul-ups wasting valuable tourney fishing time. Aswell they found that because R-bend frames have a higher blade arm angle, that the blades would spin more freely. Since a lot of these bass guys didn't use leaders back with bass fishing, they just preferred tying it on, and ended up not twisting or looping the eye of a r-bend. Again, if you're a pike/muskie guy you'll probably prefer the twisted or looped V-shaped frames, and if you're a bass guy u'll want a R-bend frame for finesing bass. Personally I prefer using R-bend frames with my bass spinners (which make them helicopter nicely), but I'll use the stronger V-shaped frames with larger pike/muskie baits for obvious reasons, which I have been. There's pros & cons (attributes) with both, I'll list them out below and explain what I found out in initial research & actual testing & tuning sessions:
V-Shaped Frames (looped/twisted eyes):
- twisted/loop eye for pike/muskie leaders
- put outs less vibration, stronger frame
- less line slip, due to twisted/looped eye
- more foul-ups due to the blade arm being closer to the body
- heavy wire diameter
R-Bend Frames:
- self corrects in freefall, less line foul-ups
- blade arm & blades are further away from body, equaling more free spinning blades
- puts out more vibration, lighter frame (depending on wire diameter)
- does have a little bit line-slip
- usually come in lighter wire diameters, but can be custom made with stronger wire.
Also heres a quick tip, I never did this, but if you're using a leader and if you really want to turn/convert a r-bend into a spinnerbaits, just put a skirt collar over the bend or better yet you can also tie the bend with wire or thread.
Spinninreel, sometimes I will on a particular lure, after a test session I might modify the lure, but usually I won't do it there on the spot as I hate bringing all the tools & small parts with me etc, but what I'll do is experiment and take notes or write down descriptions of how the lure looked in the water, add ideas for a better parts or even better blade selections.