The following statement is a review about weight tubes by someone off of 3 rivers website, and I completely agree with them.
"I suppose if you need to increase your mass weight in a hurry, without buying new arrows this system would accomplish that. But if you want to stay w/in proper FOC percentages, and consider proper dynamic spine in your tuned arrows, these tubes mess with all that. I don't understand how this item ended up in a traditional catalog, This item may work well for compound arrows. I think if you are serious about your arrow tuning and want a heavier arrow, get shafts at the proper weight and spine."