tyre sealant is tyre sealant, probably cheaper from ebay mate. you dont really want to use that stuff unless you can help it as once its used the tyre is unrepairable and has to be binned. easier to get recovered to a tyre center if its fixable and pay for a repair... alot cheaper than a new tyre thats for sure!
my tyres are insured against puncture until theyre down to 2-3mm so a free fix if they get snagged
If VW service the car they check the sealent and replace it if its out of date. Mine was serviced yesterday (47,700) and they replaced it. But I too have been told not to bother just get the wheel to a tyre centre and they will do it.