I installed the SLS front and side mounts last night. My other mounts are stock. There is definitely a noticeable increase in vibration, but only at idle. The vibration is perceivable through any contact point: steering wheel, seats, floor, but isn't strong enough to be annoying. If it vibrated like that through the whole rpm range while driving, it would be hard to deal with, though. There is always a compromise between performance and comfort, though.
The mounts perform wonderfully. My engine used to shake quite a bit when I started the car and I was getting a clutch chatter that would cause the engine to shake when starting off in first gear, especially in cold weather. The mounts eliminated the clutch chatter, so take-offs are nice and smooth. I also spun the tires on wet pavement hard in 1st gear. This usually resulted in pretty violent wheel hop, but no more.
The mounts were packaged well and the quality looks pretty good. All of the necessary hardware was included. It would have been nice to have a simple diagram of the mount assembly. It was easy enough to figure out, but it would have saved some time in figuring out which existing hardware needed to be re-used, where the washers go, etc... I am also curious what the torque specs are for the different nuts and bolts. I tightened everything to about 30-35 ft/lbs and used loc-tite on all the threads.
All in all, SLS is a good way to go if you are having problems with your stock mounts or just want a stiffer mount to limit engine movement.