Hi Dan;
I find no fault with the 2nd glass. Especially on the larger engines, 3ft etc. Two glasses was the standard on the IC for a number of years before steam was fazed out. Both glasses were in safety shrouds that contained the broken glass and vented the steam below the deck in case of failure. And if one failed the crew still had the other to go by.
However, there are still some of us running the
small engines, 15" etc. who have to depend on 1 glass and try cocks. Keeping both clean and in good working order is a must if safety is included in your plans.
I would not want to be setting with my feet practically in the fire box door of a 15" engine when the crown sheet dropped. I am pretty sure it would not be a comfortable occasion.
Jim