I've used them. Yes, they are as puncture resistant as they claim to be. And, yes, they are heavy (look at the tread - they have huge knobbies on the sides, plus the very thick slick in the middle) - but they are Dutch tires, made largely for the Dutch/German market where people bicycle to work and back each day on flat surfaces. But I would not recommend buying these. I had two of them - both on the back wheel - and both of them blew out the sidewall. I don't think the sidewall is very strong. I switched and have now used Schwalbe Marathon Plus tires for 6 years now, and I swear by them - never had a puncture, and never had a sidewall blowout (oh, by the way, the Vredestein Spider Max sidewalls both blew out in less than a year of use - something wrong there).