Hi Neil, mines up ten yrs now and after five storms and a hurricane I’ve not lost a slate yet !!
Price savings on slates are counter balanced by additional cost of clips.
But the real massive saving is cost of the labour. My lowest quote was 15000 for a conventional roof including the slates.
I did it with a roofer friend in five days.
System cost me 6k. Labour and paslode nails another grand. 7k all in.
The aussies state you can walk in the roof !! Load of bollox, you can NEVER walk on a nu lok roof. Also they provide 3clips for every 2 slates, but I discovered half way thru, 5 are needed.
Apart from that it’s a magic system and I can see why roofers hope it never takes off.