I don't have a much experience with the arrows, but just got some last week from The Bow Rack and was sold my first time out. In fact got in touch with Chris (OR Archer) today for another dozen. I have previously shot FMJ's, but have most recently been shooting 340 A/C/C Pro Hunters. I shot the FMJ Injexions side by side my ACC's and the penetration was a no brainer. Then I shot the best 50 yard group of my life and decided right there to make the switch.
I was shooting the A/C/C's because I still really like the HP inserts over the HIT or D6 because I have had experience with mushrooming the end of the shaft on my FMJ's. I also like to index my broadheads with the fletching, eventhough it probably doesn't make make a difference. When it comes down to it though, I'd shoot a glass arrow if it offered better chance to kill...so if I lose an arrow here or there I can live with it.
When you look at the FMJ Injexion vs. the FMJ, there are also some numerical advantages. Smaller diameter, which in theory should have better penetration and less affected by crosswind. You are also getting a lighter GPI for a stiffer spine, with the same construction as the FMJ. Depending on your preference for speed vs. weight, that may be good or bad. I still like to shoot fast, so thats an advantage to me. Inexions also have a lighter nock and a heavier insert. Its just a few grains, but mathematically speaking thats improved FOC built right in.
The Inexions are probably just a hair better than the FMJ's for the reasons listed above, but not sure if justifies making the switch for everybody.
The broadhead thing is a little disapointing. I've shot Montec's with good success for the past few years, but heard lots of great things about the Trocar so I look forward to giving them a try.