Injexion sized arrows are the thinnest diameter from Easton, but require deep six broadheads and field points to fit the smaller diameter threads. They come in a A/C and FMJ model and the deepsix inserts are supplied with the arrow. Those who don't want to invest in changing broadheads usually opt for something like the easton axis or regular FMJ. All are good arrows. I've toyed with easton Bloodlines, FMJ's, A/C/C Pro Hunters over the past few season, and althogh all had good results I really like the Inexion FMJ's I"m using now.
There are lots of different ways to build arrows, and everyone has their own opinion on what works best. Lots of debate over weight, FOC, broadhead, etc, etc. Ask a dozen people and you will probabloy get a dozen differen answers.
All I can say is you don't NEED an aftermarket insert/outsert unless you want to add weight or try to run standard broadheads in an Injexion sized arrow. Still confusing...I know.
My advice, without knowing all your specs, would be to try the Easton FMJ if you want to keep using your standard 9/32 broadheads and field points. If you want to give the injexion sized arrows a shot check out the Deep Six FMJ and Muzzy Trocar combo. Build either arrow with the easton inserts supplied with the shafts and you'll be just fine.