Well, I took that figure from memory...
As I stored those flashes away already, and as the dedicated feet are stored with cameras, I took 20g as an estimate for a dedicated foot.
Then that 100g gain comes true for the Cullmann flash (2 reflectors, one with single-axis swivelling).
For the Metz (1 reflector, 2-axis swivelling) the weight gain indeed is only 50g.
Of course the true weight difference should be taken with the batteries loaded (4 AAs with all those bigger flashes) and then the relative differences are less, but still it shows the weight range from tiny to advanced TTL flash. (But it seems the tiny ones are all too dedicated and not adaptable.)
It this context I wonder why TTL is such a prerequisite. With just thyristor controlled autexposure flash there is a choice of really tiny flashes.