ScoobieDooo once bubbled...
What would be the advantage of taking a DIR:F course, adopting the DIR mindset, diving principles, gear config, etc. if your diving friends do not subscribe to DIR as well?
One thing to keep in mind is that "DIR" is just a label for a very solid system.
It is not ONLY about equipment, as you will learn in DIR-F.
Your benefits will certainly depend on how DIR your buddies are, and even if they are wearing "stroke gear", they could still hold to some or most of the non-equipment related aspects of DIR.
You may want to ask if your buddy will benefit from you being (mostly) DIR if he is not...
You will ALWAYS benefit from the streamlining and comfort that the equipment config provides.
You will ALWAYS benefit from the increased comfort and self-confidence that you will feel in the water.
Go back and look at Rule #1, and the definition of "stroke"... George and JJ have slightly different phrasing... a stroke is an unsafe diver, and a stroke is a diver with an unsafe attitude.
Stick with rule #1, and it doesn't matter if your buddy is wearing split fins and a poodle jacket.