Boba U4's have softer cushioning on the bottom and a quieter slide over the tactile bump, making it noticeably quieter overall. Silent Bluish White are less mushy, so when you bottom out a stronger shock will be transferred to the plate and the keyboard build and materials will have a lot to say about volume and how that shock sounds.

In my quest to try out most sound-dampened switches on the market, what I'm really looking for is a switch with low-volume (quiet, not necessarily silent) that still sounds good. In this regard Boba U4 doesn't score well because I think the sound it makes is a bit thin and flimsy. Put them in a well dampened keyboard however and you have a very silent and enjoyable feel which no other high-tactile switch I have can match so far, including TTC Bluish White, Haimu Whisper, Durock Blue Macaw and Kailh Deep Sea Brown.