I have two separate experiences......

First one was okay - lasted as long as it took for me to break other parts of the engine (say about 15k)

Second one not so good. As has been stated a lot - they are good when both the head and the block are in perfect condition. If not, forget it.

To put this in scale, there was only one incredibly minor perfection on my cylinder head adjacent to the water jacket on the exhaust side. Whilst I cannot confirm until I get the head off, it is my opinion that this minor imperfection has led to my gasket failure. I will confirm when I take it to pieces tomorrow!

Cheers matey

JJ