My 2 Pence,
When buying studio lights, like your camera your buying into a system, and accessories, the reason I would not touch the Interfit EX models is there is no ability ro expand, the number of accessories is very limited and you will soon out grow them.
Best bet is to go for the Stella range if you are looking at Interfit, as it has the S TYPE fitting accessories which gives you all their options, many cheaper non brand options and everything that fits Bowens Gemini lights!
That and the fact you have a wide choice for expansion also means once you have mastered one accessories you can move to another, your not limited by the heads!