Some more specs and food for thought.
Battery pack:
The Witstro's battery delivers 450 pops at 360w, whereas the Xenergizer delivers 650 pops at 400w or 450 pops at 600w.
Weight:
The Witstro AD-360 weighs 27oz and its battery pack weighs 18oz. for a combined weight of 2.8lbs. The Xenergizer pack + battery weighs 6.7lbs. Couldn't find the weight of the Xenergizer head, but after you remove the grip handle it's likely well under a pound. So, the total kit weight of the Witstro is a bit under half that of the Xenergizer. The suspended weight of the Xenergizer head is a bit under half that of the Witstro. There's one other thing to factor in, though. When using a softbox or beauty dish, the need for a speedlight/softbox bracket with the Witstro increases the size & weight of the Witstro kit and the suspended weight of the head assembly by almost a pound. With the Xenergizer, lightweight mods can be attached directly to the head.
Setup:
Attaching mods directly to the head is simpler than putting a speedlight on a bracket and attaching mods to that. Depending of the nature of one's work, this may or may not be of consequence. When I have to start at 5am or rocket through an impromptu VIP portrait session in 10 minutes, simplicity of setup counts for a lot.