I feel it's almost simultaneous, but I like to stab the throttle and pull the paddle then get off the gas a bit so I have the lowest gear ready.
When you hold the throttle down and pull the paddle to accelerate, there isn't much of surge or feeling of acceleration IMO. Feels very much like a regular auto in that regard. Either way, I think it would work much better without the detent/click point.
One thing I don't like is that right at 80, it gives you 4th gear instead of 3rd. So not the lowest gear possible. Just under 80mph though, you can get 3rd gear.