I can tell you, these sparks are quite noisy! Keep you children (and yourself) at a safe distance!
Never attempt to energize such apparatus at your home!
With the given 0.5 mA supply, there is a spark every few seconds. Triggering is nice, and stage voltage reaches about 23-24 kV – the design limit.
Should you ever operate a Marx generator, make sure to properly ground and short it prior to approaching it any closer than a few feet!