I've used the same 12v/100w Dedolight kit for over twenty eight years. The transformer can simultaneously power four Dedolight heads equipped with 20W, 50W, 100W or mixed wattage lamps. Dedolights in this voltage are no longer available.
The 24 volt transformer has three outputs and this output is higher at 150w. The lower power consumption of the 12v/100w kit was good for working in places with dodgy power (Africa and Asia & Sth America) where there is often only a single output in a tiny home.
Certainly the output of the 24v/150w transformer is brighter than the older 12v/100w model and this aspect is better and more valuable at times, however I've found so many shoots where I want to run four lamps, and the 12v/100w version did that.
However, that is not a huge consideration, I'd prefer to go for the 24v/150w kit using a central transformer - you can put 12 volt lamps in the lamp heads to run from car batteries, gel cell packs or camera batteries etc. The DT24-1 in-line electronic/dimmable power supply also works with the 150w heads so you can purchase additional lamp heads as you go along.© 2013 Pieter de Vries ACS