I've been using Orijen for just over a year now with 5 (+ 1 newbie) cats........
One major caution for you...go extremely slowly with your transition (I presume you understand the need for a transition vs a "switch" - if not, post back and you'll be advised). You're obviously aware of the high protein/high fat/no grain/low carb content...cats who have grown up on grains can react poorly to this type of food at first. I started with (literally) just a few pieces of Orijen mixed in with their previous food, and each day, added a few more kibbles...it took two or three weeks to reach the 100% Orijen bowl. (The "newbie" arrived three weeks ago - he was transitioned in the same fashion and is now 90% new food.)
Watch the litterbox - if the stool becomes soft, stop the increments until things return to normal, then resume, perhaps even more slowly.
I've recently added in Wellness Core, and I've had to follow this same procedure - there was some soft stool, so I leveled off for a week and then resumed with tiny increments. Patience needs to be your guide. My goal is to attain a 50/50 ratio - I'm almost there.
Also....when I first received the Orijen, I presented it as I would a "treat" to judge their reactions - everyone turnd up their noses and walked away! So, don't use that method to "taste test" the Orijen.
(When I did the same taste test with samples of Wellness Core, I received the opposite reaction - they literally cried for more. Initially, that worried me, because typically, manufacturers spray kibble with restaurant fryer oils - to increase what they call the "palatability factor". Orijen isn't treated like this, according to the manufacturer - I guess I proved that in my own "taste tests"...and, while I still wonder about the Core, I'm sold on its ingredients.)