Played with the VC100.21 hit with and without the 8g butt cap change to change the balance.
Playing specs: 317g strung VC18Lg/PRCW18g, then + Wilson Pro overgrip + silicone band= 325g + 8g butt cap replacement.
Balance: 332mm strung stock, 321mm as tested.
Can't really compare to the VC100.18 because I only hit with that one for about 2 hours. I have recently tested the EZ100.20+ which played stiffer than the VC100.21, which was very surprising. It also felt very muted like the EZ series. The VC100.21 does not have the same treatment of a thicker beam as the VC98.21. I remember the VC100.18 to play firm but not stiff. The VC100.21 is noticeably more powerful and spin on the serve vs the VC98.21, but not as pronounced a difference in power as the EZ or VC.18 series 98 vs 100 ranges. I believe the softer frame has lowered the power a bit. It basically is a softer and more muted model vs the older one. I think it still has the forgiveness and nice whippy nature (even without the extra weight I added later). Still it isn't stable at the top half of the hoop once the pace picks up, and probably needs 3-4g @ 10/2 to bring up stability. The string bed is bouncy, even more so than the EZ100+.20. Could be the spacing or flex.
I'll write about the VC95.21 last since I spent the longest time with this frame in the last 4 days.
Just don't use the Youtube translation in front of kids. It had some of the most lewd translations of Japanese when I last watched their website! LOL