An important thing to remember is that if a substance was not formulated for 3D printing, all bets are off. It might work. It might clog your hotend. It might off-gas something toxic and kill you. This has been mentioned before when people were printing with weed-wacker line (because it is cheap and mostly nylon), but it turned out to contain fiberglass. So there are a lot of risks.

Related to that caveat: I would never melt (or even excessively heat) a synthetic polymer that I didn't know a LOT about. This EPDM rubber is not a natural rubber, and it could break down into a dozen different things to give you cancer or kill you outright. But I think this is a moot point because it looks like this EPDM rubber is a thermoset and wouldn't work anyway.

If you decide to buy some anyway, I recommend taking a small amount of it and gradually heating it up on a hotplate or a stovetop and seeing if it smokes or smells ungodly before melting or smoldering. And if you decide to try printing with it anyway, buy an extra extruder.

The moral of the story is: Please don't kill yourself to save a few bucks. If it doesn't work, you'll probably end up spending the extra money anyway.