Optane memory is used to implement a high-speed cache that will accelerate the performance of a (spinning media) HDD. Its effectiveness is dependent upon the types and feequencies of accesses that occur to this drive. Its highest effectiveness comes when the HDD is the system (boot) drive. Its lowest effectiveness is when the HDD is a data drive.
You have only one M.2 slot, so you must choose to either keep your SSD (which is one of the faster SSDs available) or discard it in favor of using an Optane module to accelerate the performance of a secondary HDD. To me, this is a no-brainer; forget the Optane module.
P.S. A secondary frustration for me is that Intel Rapid Storage Technology (RST) used to support a feature called Intel Smart Response Technology (SRT), which allowed you to use all or part of your SSD as a high-speed cache that will accelerate the performance of a HDD (gee, sounds familiar). Of course, when they introduced Optane, they conveniently "broke" SRT so that (I presume) it wouldn't compete with (and thus hinder the sales of) Optane.