The restrictor "limits" the amount of lateral movement on the center point of the bridle attached to the leading edge. You may like it without, as it's more similar to a stock bridle's wiggle-waggle.
The "afterburners" kick in when the kite is powered up and you want even more acceleration (huge surge of power forward regardless of the handle/leader tuning). They further distort the frame to capture more air pressure. Usually most of the energy is transmitted to the parameter edges of the kite frame. The attachment point to the tops of the down-spars is where you may see slack (say you were standing under the kite as someone else flew an inverted hover over your head). You can fetch-up tighter during the installation process (double wrapping the end=cap with the attachment loop on the tops of the down spars) or you can leave it as a single wrap (as most bridles are installed)
All the bridle attachment loops should enter the end-caps from the center of the sail, outward. You have more legs too, so you are spreading the stress over a greater surface area
I've probably bought 3 dozen of these FB string things, mostly in the 1.5 size. I crafted the installation directions and advised Will Sturdy on how to pkg\deliver the product so it's easily installed by anyone. I've given him specific kites to fit the bridle to as well. I didn't come up with any of this stuff, just adapted it for my own usage.
I was at Huntington Beach this past weekend and David Hathaway (Monkey, Team I-quad) had a go on my modified Zen. I was using it almost exclusively for 5 days since the wind never got any higher than 10 mph. He laughed and said his is tucked in a corner of the residence and never used. I've worn two of them out & couldn't imagine a better solution for low/no-wind! Jeff Burka figured he'd never need his, so it was left at home in DC. Both of these fliers are master-class holding box stock Zens and it's not cutting it performance-wise. Both found my wing much more enjoyable, instantly.
I've heard about hybrid mixed frames, but a Zen with a diamond frame is the hot set-up, PERIOD Since I fly very aggressively, I prefer a Travel Frame of diamonds, I will break sticks and I only want to replace a short piece on-site.
The french bridle alters the bending of the frame compared to what you are used to. A stock bridle bends the frame in the center. The french bridle bends on the outer thirds of the leading edge first, if you kick-in the afterburners also you are distorting the center portion slightly as well.
You don't need all the crap on my kites, but none of it is a detriment to low wind flight. If you were only going to do one thing at a time I'd say to add the Magic sticks first, (dramatically alters the glide) then the french bridle (more responsive to pilot commands), thereafter you are making the kite differently during it's construction. A tighter fit between the leading edge sleeve and the spar (only one tube fits and it's snug too = a tighter and more efficient sail). As for the extra reinforcing patches built into the leading edge sleeve? That is how the highest-end kites are made by Bazzer and Shook now, proven to double the lifespan of your kite. (the part that wears-out now for me is the trailing edge)
I might be willing to buy your old unused Zen, but I really like getting a new one from Revolution after BAzzer makes the sail and Eliot crafts the leading edge. Barbara told me on the way home last night she "understand" if I needed another replacement sail, but it's a definite "NO" to an early retirement for me. <LOL!>