The PX-230A isn't a real Plextor model - it's a rebadge,
and therefore it can't do Forced Unit Access like numerous true Plextors can.
But when it comes to Secure ripping,
when caching can't be disabled on a particular drive model, the Secure ripping routine "defeats" the cache (the cache goes through a continual cycle of filling up and being re-flushed). This is more taxing on the life of a drive than Forced Unit Access (where the cache has no role), and slows down the ripping process - but achieves an identical rip in the end. This is actually how 99% of people do Secure ripping, even when their own drives can do Forced Unit Access! (because they don't know what their options are - they're simply following an easy-to-find Secure ripping tutorial made by someone who has probably never owned a real Plextor)
Ironically most of the few people who learn about Forced Unit Access, are not true Plextor owners, and are disappointed to find that their drive models can't do it. If you go to the dBpowerAMP forums, you'll see people asking about Forced Unit Access (because it's a more easy-to-find option in dBpowerAMP than in Exact Audio Copy), and the repeated answer is always "It's for Plextor owners".
I think you'll be okay. I have the Rosewill version of the PX-230A (which doesn't pretend to be 'Plextor' at all), and it's been doing cache-defeating rips just fine.