How many guys were there? He has to pay insurance/maintenance on the van etc, liability insurance. It's easy to say it's only half an hour but you need the knowledge to do it properly and cover expenses.
Yeah that's a lot of BS, we've had the same issues in Scotland with that felt. On slated roofs we don't have battens and it's still an issue.
Just a cop out from them making a shitty product.
I've got a carters one, roughneck ones are also decent.
For slate hooks https://www.burtonroofing.co.uk/black-coated-80mm-spiked-slate-hook-316g.html
You can get them in different sizes too.