Apart from the change in colour, and the foul pungent smell it has now, I can't tell any difference from the old stuff. I'm actually finding it easier to smooth and it seems to hold the heat for longer which is good because it gives you more time for modelling.
I bought some of Gary's 'Mist' wax which is one he does that has similiar properties to Casteline, although I've yet use it properly except for just playing about a bit so can't really comment.
Personally I can't be doing with the whole sculpey to wax business. For one it's too expensive, for me anyway, two I can't sculpt in Sculpey
and three, well, I just couldn't be arsed having to mould and cast everything.
But like the big Dawg says it's all down to personal preference and what you intend do with it... But when I look at his stuff I think I probably should be learning how to work in harder waxes
Best bet is to just get your hands on some and see how you get on with it. And if you don't like it send it to me