I recently set up 3 arrows with them. I had 3 Easton FMJ that were damaged at the ends so I cut them down to account for the extra length that the Nufletch has and reduced my field point from 125grn to 75grn to try to bring overall arrow weight into closer alignment with my regular arrow set ups. I have shoot these approximately 100 times or so and so far they are working well. So I would say that if you have some arrows laying around that have been damaged then this may be a way to get some added life out of them. I say this only if you can remove all damaged area of the arrow. I don't know that I would look to use these on new arrows when I was setting them up unless you were looking to bring some extra weight to your set up.
As for some of their claims:
yes it is quick and easy to change fletches
I see no real difference in penetration
as for "fly flatter, hit harder and tighter groups" I have not experienced any measurable change in these areas.
Also you may want to look into how these change your FOC and arrow spinning. May have a negative affect. You will also, in all probability, need to go with a heavier head due to added weight on the end.
Hope this helps and if you have any specific questions I can try to answer those.
