Probably none. Humbucker bobbins are an entirely a different shape/design than a single coil pickup. True velvets will give a typical Fender single coil tone, Red Velvets are more strident tele like, with the plate on the bottom of the pickup. The FS1, is an overwound single coils with a stronger mid punch, which is a thicker sounding single coil. This makes a nice pickup in the bridge position, not wimpy and tames the high end of a vintage single coil. I have the FS1 and I think it’s great. It’s 14K resistance, but that’s do to the thinner gauge wire. It’s not a hot pickup, but it will hang with a Vintage output PAF.