mean a whole lot in a vacuum.
If you have low conversion rates, but it's due to most your 3rd downs being 3rd and long, then the issue isn't your 3rd downs as much as an inability to move the ball on 1st and 2nd down.
Likewise, if you are a team that never punts the ball and your strategy is to get to 4th and short, then your conversion rate on 3rd down may be awful.
Luckily, both are data points that are fairly easy to figure out.
The one thing I will say about our 3rd down calls is that I find it interesting that the vast majority of our 3rd down throws on Saturday seemed to be pass completions that were well behind the line of scrimmage (like 4-5 yards behind the sticks). I can't figure out if the play calls are intentionally doing that and trying to get the receivers to "make a play" and get the yards after the catch, or if we are simply checking down to open guys because the only open players are those who are near the line of scrimmage?