If unmodified, the vibration will drive you crazy. To reduce vibration, grind the base of each bushing to the same size as the OE bushings. There needs to be just a little visible space around the bushings when they’re set in the mount. This allows for radial expansion when the bushings are compressed, and it will reduce vibration without compromising performance.
From a performance standpoint, these bushings greatly improve the feel of shifting in both manuals and automatics.