I put Trifecta on my Redline. Just flash the car with the new code and BAM! massive power increase. No hardware changes.
As for tiers, they have options for using different switches in the car to flip between their tune and the stock one. You lose whatever function that switch used to provide, of course. I didn't have a need for that so I picked the tier that can't be flipped. I'd have to flash the OEM image back into the car if I wanted to do that. Also, I recall they have an option to pay them to do a custom tune for your particular car, based on your personal needs.