I use this stuff mountain biking all the time and it works great... Many of these products are just ground up paper in a substance similar to glucose and water (think paper + personal lube smoothie).

It'll seal just about anything in your tire and it will seal any slow leak that is on the tread of your tire. When spinning the wheel will balance out pretty quickly (with in the first 10-20 rotations or a couple hundred feet). I'd assume it would balance out even quicker under more power.

In our case, since these are water based products, I'd assume they're also not tire pressure sensor friendly.

I've never used these products in a car, because I've never had to, but...
Keeping in mind the unsprung weight on a bicycle is much less than that of any automobile, and I've had my bike over 50 mph without vibration...

Could the speed limitations be in place to reduce manufacturer liability for blow outs from some clown driving 120 mph with a train spike in his tire?