When I first came here 4 years ago I naively made some comments like I was on Reddit. My comments quickly got downvoted and I started putting more thought into my comments, only commenting when I had something interesting to say. The (very) harsh downvoting culture here does a good job of keeping low-effort comments out. That has been my experience at least.
You get a captcha sometimes when signing up, probably depends on how dodgy your IP is perceived to be.
They have duplicate link detection in place and newcomer post will not appear to public.