I was lucky enough to try one last weekend, and was very impressed!
Yeah, there’s a wee bit of a lag between button and actuation, but I don’t imagine it’s any different to shifting gear once you get used to it.
The only thing I’d like to see is a shifter style lever/button. Not necessarily a proper lever, but just something placed down there so you don’t have to bring your thumb back up on to the bar to activate it.
Other than that, it seems really well made and very reasonably priced for what it is.
It’ll be interesting to see how it fares through a British winter, to see if they’ve done a good job of the sealing…