First off, Eastwood, thats awesome! I' m currently on the floor l.m.a.o.
Anyway, to answer the question, they are a rest that encircles the entire arrow but allows the fletching to go through. There' s no doubt that they probably slow down the arrow a little (any form of drag will do that) and also they are a little hard on fletching. All that considered, I DON' T CARE! To me it is priceless to be able to sit on the stand with an arrow nocked and my bow laying across my lap not caring if the arrow has fallen off the rest.
They are also very accurate! I switched to one before 3-D season this past year and was really impressed. I still shoot a prong rest for indoor competition due to the fletching issue, but for hunting I will re-fletch the couple arrows that tear veins for the convenience I gain.
I was going to give my 2 cents worth but it turned out to be more like a buck-fifty...
Ben