Jordan, the Apex version began to be used in recent years by Aqualung (after the parent company acquired Apex) to replace the original ones that were used for many years. The original silicon diaphragm had a stainless steel plate instead plastic, and was at one time available in both clear and gray silicone. Your Apex version is likely made of silicone and if still soft and pliable it should be fine to use
I think the original type are still used in the military version of the Conshelf. The last time I checked they were listed for about $30 retail.
I have a good supply new original types that sell for much less. You can contact me through my email link for more information.
The older I get the better I was.