The blurb on the product page (LINK HERE) says :-
"Will K-Seal ULTIMATE damage or clog my engine?
No. Part of the strict requirements of ASTM D3147 is that a coolant stop leak product should pass through a filter of 0.85mm without clogging or gelling. This ensures that the product will not block even the narrowest passageways in the cooling system. "
From reading the rest of the blurb, it may be a better product for leaky WBX head seals (though still not a proper job I grant you)
It is expensive at around £38 and you might need 2 bottles for our large capacity cooling systems (citation needed there) but they offer a money back guarantee. Apparently, if after using it, you then need to have a "proper repair", all you have to do is send them a copy of the receipt for the repair and they will refund the full cost you paid for the product. That seems fair enough.
