One thing that was not mentioned is the boosting durability. FCL seems to have the longest impact time. OVerall, FZL, Kailin, and Yellow oil are the best three.
Svis is called outer w968 by some users. It is indeed similar to W968 in some ways, huge support, catapult effect,... But it is way easier to play with than a W968
I bought several times from prott and had no problem. The shipping might be long due to custom clearance in the US. ALiexpress might have fast shipping speed sometimes.