I just called DAA today to order an insert for a CK steel grip. The guy who took my order recommended me the STI insert, so I took their advice and ordered it.
Then, right after a few minutes, I came upon this thread and another thread that has an email quotation from Saul Kirsch:
https://forums.brianenos.com/topic/237165-holster-info-for-ck-arms-2011/
So I called the DAA again to talk with one of their techs to confirm on this. His initial response was that STI should work fine for CK arms steel grips, so I asked him if the SV steel insert wouldn't be a better option as the STI insert could be too sloppy for the CK steel grips.
He said the gun might wiggle a little bit in the STI insert but it shouldn't be an issue as the gun gets locked up as it is sitting in the insert, so the gun won't come out. He also said he finds that a tiny bit of wiggle shouldn't be a problem in general as he personally owns an insert like that as well, and he has been fine with it. However, he still offered swapping the STI to the SV steel insert, so I told him go ahead and swap it as I am hoping it to provide a better fitting after all.
I'll update when I receive the part and finish the fitting process.
Thanks,
J.