I used to work for a firm that only dealt with them , was never down to the workers if the glass got scratched , bosses insurance always paid out , thing was , we were always carefull , but somehow the glass was always damaged according to the site managers !
Not done one since i have been on my own , but if i ever do get asked it will be a huge quote , and i will have a written stipulation , due to the nature of the work scratches are not covered by my insurance !
Thats the only way i will ever do one !
Rich P @ F