I purchased some GATOR BITE fittings which have plastic inserts. Sales person told me that if using copper tubing, not to use inserts.

I also purchased some SHARK BITE fittings which have plastic inserts. Sales person who sold me the SHARK BITE fittings said the inserts must be used.

Does any one know which is the correct method?
Thanks

You must use the inserts with PEX. Gatorbite sells them separately.

Inserts used on PEX with both gator and Shark. On copper neother gets any fitting. The insert is to keep soft material tubing from collapsing.

Here is the answer straight from the manufacturer's site:
The SharkBite® fittings have an integral Tube Support Insert that is effective in supporting PEX tubing to ensure the O-ring seals correctly on the outside of the PEX tubing. The Tube Support Insert is not required when using CPVC and copper tubing; however it is not necessary to remove the insert when using these materials.
I've noticed that the white insert are much easier to remove from the GatorBite connector than from the Sharkbite units

I could not get the plastic adapters out of my Gator bite fitting. How did you do it?

The inserts can be used with copper or pvc, you don't have to remove them.