I have tried a lot of strings from BG6 to BG66 Ultimax, Fleet etc etc. Just last week I tried Yonex BG9 at 25.5 on Yonex Voltric ZForce 4U. It had the best repulsion and effortless hitting so far of all the strings I have tried. It was just RM 20 bucks with stringing. In terms of feeling, BG9 has the hard stiff feeling compared to BG66. The gauge is 0.66mm. Anyone interested can try it out. Cheap does not mean inferior.