I've been seeing more and more delta shaped designs from all the kite companies...the most obvious being the Wainman, with its short, stubby delta shape. Now I see even the latest Best Waroo has got this design. Is it just the latest fad, or something for real? PS, I didn't see all the other kite companies jumping on the "sigma" shaped kite design.

Well even Naish seem to move a little away from that. The new Helix don't look to have much Sigma left.
I have a Delta - RRD Addiction - Extremely powerful and relaunches like a dream. Not the best uh kite, but not designed for that.
The new Bandit 3 depsite being delta, look very C in shape ?

The sigma shape is pretty easy to copyright so harder for others to imitate although the new rebel has a sigma type wing tip.

As far as delta kites go you basically get quite a bit of power for the size, good relaunch and a kind of stable grunty feel. It's just a different flavour, worth trying one out to see if you like it.