Most of the police officers I know reserve vest carry for a tertiary "deep cover" weapon (i.e. a BUG to the BUG) such as a Kel-Tec P32 or P3AT. The ankle or even the pocket would be faster to access without destroying the uniform shirt in the process. In addition, most of the vest holsters I've seen haven't been all that sturdy; I don't know that I'd trust them to support the weight and bulk of a gun like a G26/27.