I've heard that too, just based off the sound in those videos though my 2-3 shift is quite a bit slower. The drop in RPM during the shift is just too slow for my liking. I can accept that it'll be slower than 1-2 shift but I still think it can be a lot quicker than it is.
I'm also looking at a Sonnax Billet Accumulator Piston as it occasionally feels like the kickdown band starts to apply when I'm driving around in 3rd gear, just the faintest sensation of touching the brakes or a gust of headwind. The current TransGo instructions say to leave the piston and springs in so that's what I'm going to do; I know it's possible to use a blocker rod but I'd rather just follow instructions for this type of thing.