A Sharkbite seal is made by an O-ring. The whole thing is held on by spring loaded teeth that can be retracted by pulling on the movable ring. The teeth are angled so it's nearly impossible to remove it without retracting the teeth. But, pushing it on can scratch the tubing. I've not taken one apart enough to tell if it is significant. In theory, I supposed it might scratch things enough to prevent the O-ring from sealing, but they do not go that far onto the tubing, so they shouldn't, even if they did scratch things. Not likely a problem on PEX, but when used on harder material like copper, if you don't clean up the edge well (they sell a tool for this), that edge could have a burr or be sharp, and that can ruin the O-ring when you try to install it. The O-ring is not replaceable that I've seen, but maybe if you really futzed around with it...time-wise, easier to just replace. The O-ring SHOULD last a long time as it's not being moved around. One side effect of using a Sharkbite fitting is that it CAN be twisted on the tubing. That will scratch the tubing, but may not get it to come off. That's likely okay on say a coupling, but may be less than desirable for a valve where you're applying torque to it, maybe on a regular basis.