It was not ripping him off, but it's not all totally true either. Is what he was trying to do is give your nephew the most forgiving set up he can have. Can you shoot fixed blades with straight vanes? Sure, but it is way more critical of tuning on both the bow and the arrows part. You better have really straight arrows, spined well and squared off inserts. Not to mention a well tuned bow for nocking point and center shot. I like a slight offset myself. Also good form doesn't hurt.

Drop aways are not the most accurate rests either per say. They do minimize fletching contact though. Providing they are set up properly. I have seen many drop a ways that have fletching contact. Off set or helical vanes are hard to get good clearance on a prong rest though, especially with skinny carbon arrows. So a drop a way or whisker biscuit type rest would work well for this.

The reasons many used a hard helical in the past was because broad heads were larger and harder to get to fly well. You also used larger aluminums in most cases so getting the fletchings thru a prong was not quite as hard. This is nearly impossible with some skinny arrows and a 4 or 5 inch fletch with any kind of helical. To be honest though a prong rest with the correct spring tension, or a blade rest is pretty forgiving of vane contact. However if you have a lot of spring tension it can be a nightmare to tune.

Feathers would also be a good choice. They impart some spin on the arrow even when fletched straight. And they are forgiving of rest contact.

I may have suggested something simular for a beginner archer. I probably would have suggested an offset instead of a helical with a more normal rest but either will work. I don't think what your nephew was told is out of line to what you would hear at most pro shops now. Other than the statement you cannot shoot fixed blades with a straight fletching. That is false. They could have worded it better.

I myself use offset feathers and aluminum arrows. I have used about every rest on the market and right now have a Bodoodle and am pretty happy with it. I do have some fletching contact though, but I am not concerned because it is very minor and I have feathers.

The best I have used for fixed blades is Nitro Stinger tapered arrows, 4 inch feathers and a muzzy drop a way. This combo would shoot any fixed blade great at any distance.

Paul