Here is a unique Skagit style spey cast that you don't see everyday. Brian loosely refer to it as T-Spey (not to confuse with Snap-T). This cast is unique in that it allows the anchor to be placed very close to the body and slightly aft of the angler. This anchor set up allows for a deeper D-loop, which explains why he say it is a powerful cast. Obviously the same cast can be executed with a Snap-T as well but the Snap-T will not place the anchor as far back as this cast, if that is important.
In Spey casting, the power of a cast is only as good as the anchor. If the anchor does not hold, all the power in the world will do no good. An anchor that slip is liken to a bow an arrow where the arrow slips off the fingers prematurely before the string has been drawn to full potential.
This cast is especially suitable when used with very fast sink tip and/or with big fly where the anchor is great and you need to muster all might to lift that anchor. Obviously you need to water clearance all round as well, not something to be attempted when standing next to a bank.