When I bought my PM9 (used) it had the XS Big Dot on it. I was not at all impressed. It's been five or six years, so I don't recall, but I either shot very high or very low with them.
For me it was very unlike anything else I owned and I did not see any advantage. I was unwilling to make that adjustment (or convert everything else over to match). I swapped out for traditional three-dot night sights. My PM9 is a keeper. The Big Dot...not so much.
If you only have one gun, and it has this sight, that may work well for you.