Gerard,
Think of it this way. A salmon "switch rod" is really a light double hand rod. A 11'6" #8 light double hander is my heaviest salmon rod, my other light double hander being a 11'6" #5 for the low water, summer salmon.
A Trout Spey is partly clever marketing, partly a nice useful trout rod. The average trout is 0.5kg but sometimes they still want a large meal. A #3 rod is perfect for small trout (and large ones!
) that want a larger, heavier meal. Want to throw a Wooly Bugger or a Sculpin for small trout and still have fun? Trout Spey!
I just wish they wouldn't call it the Trout Spey, but the clever marketing part means that they can capture the salmon anglers that use two handed rods and get them in to another market
I have an Orvis 10' #4 that throws an OPST Commando head and it is just great for small trout, large trout and anything else that comes along. It was a single hand rod until I got Sandy Nelson to change the reel seat and add the longer second handle. Some of the other guys here have just had Sandy make them light two handed rods and by all accounts they are really excellent.
So there you have it. Trout Spey = light, fun two handed rod for small trout.
Switch rod = Light two habd salmon rod.
More and more anglers are going lighter with the way they fish. Why not try it?
Euan