Some tyre sealants are going to wreck the tyre, due to the chemicals used, not all do, but a lot won't touch tyres for repair where this has been used.
Ask yourself what's worse paying £15 for puncture fix after removing the tyre to fit the spare, maybe at 3am on a pissing wet day on the M25 hard shoulder or paying £10 per tyre to make sure you never have to with a product that pays for itself in increased mileage/tyre life from using it.
I had a yoof tell me that if he took off tyres that had ever had sealant in them it would knock him out due to the fumes and he would recommend a new tyre rather than sealants, he looked a bit sheepish when I pointed out the two he'd just removed had ultraseal in them, he didn't believe me so looked then said he felt ill wtf!!
It's so harmless it is edible, makes you sick/vomit but doesn't harm totally bio degradeable as well.
tabetha