Sorry Phil that website is wrong... The guide number of the DS 125 is 32 underwater and 64 air. That is almost three stops brighter than the z240 with a guide # of 12 underwater and 24 air. You can test this by using your flashmeter and setting both strobes to full power then take a reading at exactly the same distance from each strobe.
Have you verified that the DS125 is 3 stops brighter than the Z-240? The DS-125's air guide number of 64 feet compares to the Z-240's GN of 79, the Z-220's GN of 72 and the DS-200's GN of 76. Inon's Z-240 guide number is 24 meters.
In order for the DS-125 at 110 watt-seconds to be 3 stops brighter, the Z-240 would have to be only 10-15 watt-seconds or incredibly poorly designed. That is ludicrous, of course.
Inon doesn't specify power supply capacity, but it does specify cycle life for various batteries. Z-240 specs
Inon specifies 320 cycles for four 2700mA batteries and that yields 146 watt-seconds per cycle. In other words, the power supplies for the Z-240 and DS-125 are similar in size.
The biggest downside of that test was that it was performed in air. It is not wrong though.