"thickened or senior players" reference on Roro-x spools website listings.
Two different thickness (mass) of brake rotor.
"Thickened" will provide more mag brake response, and is especially the choice on older TDZ reels, which have older, less powerful annular magnets.
Senior players denotes a thinner, lighter brake rotor, which has all the mag response you need on the improved annular magnets in late Daiwa SV TW reels.
They're using "senior player" to imply a difference in casting skill (backlash recovery skill) - some truth to that, as old style baitcasters required complete elimination of jerk from your cast (modern SV and DC brakes invite you to cast like a total jerk).
Stock Steez/Zillion 1016SV spool on the left weighs 12 g, and will cast 1/8 oz, but likely not beyond 90-100'
SV = moving rotor, the latest magforce brake.
With jerk and acceleration, the brake rotor rides a ramp deeper into the mag field against a spring - when forces equalize in the spool, the rotor retracts to linear mag brake.
SV is a "nonlinear" mag brake that duplicates centrifugal brake function at start-up (and costs less distance in the rest of the cast).
The Roro-X spool with titanium spindle and fixed brake rotor weighs 5 g and I'm casting 2 g to 130'
It's not measurably heavier filled with braid, and inertia is so low, it doesn't need SV up to a heavy lure weight limit.
If you add enough jerk to your cast, it's possible to get a start-up backlash, but certainly less likely for a "senior player"
The fixed Roro brake rotor turns the Daiwa SV into a simple linear mag brake. I also have the Ray's Studio Honeycomb SV spool, which adds the start-up jerk forgiveness, and raises the lure weight top end. The SV complication adds 2 g to the Ray's spool, but also turns it into an All-range braid spool, effectively without an upper lure weight limit.
Side-by-side casting in the back acre, the honeycomb SV costs just a slight distance on the low-weight end.
I got here by no one making a BFS (microcast) aftermarket spool for Lew's, and also not wanting the small spool diameter that's typical in off-the-shelf BFS-ready reels. After research, and seeing all the wonderful aftermarket spools out there, I chose the Daiwa Steez/Zillion route. My niche was not really stream trout, or even bass fishing, but distance casting tide passes to imitate winter glass minnows. Stock varies with batch manufacturing, but both Roro and Ray's, also Momo (AMO) offer BFS spools for Daiwa Tatula and Abu Revo.
The way they do linear mag brake on Lew's and Revo, the magnets are in the palm plate, and act on the flange face of a deep spool.
Aftermarket BFS spools are also out there for Abu Revo - they keep enough differences in spool design that none will swap into Lew's. With the basic Revo mag brake, the BFS spools add a brake-face partial flange. These are ZPI Alcance spools, 7 and 11 g, machined magnesium plus titanium spindle.