I have heard the Herron phono preamp, but not in my system. It is a giant killer. I know it retails for 3800 dollars or something like that, but it actually compares to much much more expensive phono preamps.
I was actually going to purchase the Herron VTSP 3A, but a mint used Vac Ren MK3 with built in phono came up on audiogon, so I jumped on that.
However, I will fully admit that the VAC was as much form lust over function.
I wouldn't hesitate to give the Herron a try.