A woman I met recently has one and raves about it. Loves it. She has 3 small children and so the 2 younger of them go in that.
We got the Slalom Pro (single buggy version) and it was things like the tyres being airfilled and able to pop off with a single button click etc we liked. And the frame is easy to clean etc.
Was never keen on the Rebel pro infant carrier so we skipped that bit, but for the twin I think they are good. Just depends if you need a lie flat pram etc.
I find our single one really easy to manoeuvre and so on and the other thing I like is that all the orange buttons *do* something. Adjust etc. If its not orange, its not meant to push up/down etc.