Great comments on this, and with all things fly fishing, there's a "right place, right time" for the Trouser Worm. I believe that it's a fly to fish when you can begin targeting carp, with the expectation that the cast has to be in front of the school.
McTage mentioned that he (like DC) will skip the tungsten bead altogether and fish the pattern with a light bead-chain only. I know that he also fishes it more in slow-moving rivers, so those are factors to consider. The foam version may prove more effective in ponds/lakes, with more weight useful in moving water.
The other area to keep in mind is the color. The original is red, and black is one that I recommend in off-color situations (sounded perfect for your situation, DC...I wondered if you hit one or the fish just simply were that aware).
***Barry, using a helicopter method is absolutely useful on larger dumbbell eyes. You're right that with bead-chain, there really is no need because they are secured with a heavy thread over thin wire.
TC