They are hit and miss, same with the flames. You'll only know if you have a problem if you try one and observe something. Most potters and flames are usually 75% safe (a statistic that I just completely made up all on very own!
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I have had one for years. I have never observed any nipping on either corals or clams. However, that said .... I have not been able to keep SPS of ANY kind for about the same length of time. 2 + 2 = ?? I'm not sure. It's a coincidence hard to ignore ... but it could just be coincidence. Drawing a parallel like that without hard evidence is called Texas Sharpshooter Syndrome.
For sure, the clams have been safe though.
My advice is go for it, but be prepared to change your mind if you have to.