I don't use it in .38 Special, and never have IIRC. But, Clays is a good powder when used sensibly, so it ought to be pretty good for lower pressure, target-type loads. I wouldn't try it for +P or greater loads without further research and/or testing.
I use Clays for 125gr plated target & 140gr lead cowboy bullets with great success. Very clean burning. Just be careful not to over or double charge the powder. Given the case lenght and light loading it may be difficult to notice. I also us it for 45ACP & 45Colt.