There's not enough drop in 40 yd. to compensate for with sights. As far as whether the extra equipment being worth it, in all cases, you'll end up with a better pattern with an extended turkey tube than a factory flush full. They are expressly designed to be used with turkey loads.
Undertaker is a good tube. I use one myself. The board is full of reports of good results with them. With some patience and experimentation, I'm sure you'll find it was worth it. Have fun with it.