Hi and :welcome:
Here are some great threads on using teflon with vinyl. You'll get a variety of answers and reasons why folks say yes and no.
T-Shirt Forums Search Results
Personally, to me, it's not going to hurt anything and guarentees your press stay squeaky clean. If it's a concern, it's worth getting one.
Also, if something does get on the upper platen, there is a product called E-Z off platen cleaner. That is NOT the EZ Off oven cleaner from the grocery store. This product is for cleaning upper platens.
It might be a good idea to buy some to keep on hand in case of an emergency. It's relatively cheap, about $10, and if there is an accident, like someone forgets to use the teflon and for some reason, something gets on the upper platen, you'll have the stuff around to quickly reverse the mistake and keep production rolling along without skipping a beat.
It has taken folks hours to clean a bad mistake on upper platens.
Haha, no doubt!