Do not use it as a preventative. And only use it as a very last resort.
It never goes hard on the inside and will always remain as a liquid. It can cause balancing issues. More seriously it has the ability to rot the tyres from the inside. MORE seriously, if an object punctures your tyre and it seals it. How are you going to know your tyre has been affected. How are you going to know the inside belts and cords have not been damaged?? Not worth thinking about is it.
Less seriously. If it does half stop the tyre going down. You know you got a puncture, and want to get it reapaired. You wont be able to. 99.9% of tyre specialists wont even contemplate cleaning that shit off a tyre to repair it.
Your best bet if you are that worried is to buy a self repair puncture kit and some AA cover.
The facts I have stated above are backed up by a few manufacturers on this site.
Ultraseal. Ok in cars. Do not consider for bikes.