I put the Alpex 4k against the DNT Zulus 4k the other night in darkness in admittedly terrible conditions and the Alpex won with a better picture in both IR and non IR. (I'm not in any way saying the Zulus is a bad scope, it's more than capable but the Alpex deffo had the edge).
What concerns me about the Pro is the swapping to an F1.8 lens (same as Zulus) over the Alpex 4k's F1.2. Their advertising it as a "F0.9 equivalent" using algorithms etc, but in reality nothing really beats the light gathering capabilities of a low f-stop lens. We may end up seeing that the Alpex 4k beats out the Pro at night/low light.
Why does this matter, you may ask? Well, it probably doesn't - all these scopes will be capable in their own right, it'll be down to the slight picture and ergonomics differences/preferences of each user.