I've used the shark/gator bite fittings before. They are expensive so you'd never plumb an entire system with them, but they're great for a couple of things. First, you can remove them with the removal tool (like 75 cents) if you need to disconnect for any reason. Second, they allow you to transition two types of material together. I went from copper to pex with mine, and put 2 of them on my water heater because we tend to go through them relatively quickly out here (electric). Makes my next water heater install literally a five minute job.
Everybody I've talked to has had good luck with them-