Its something you would have to just try for yourself. It works ok, well, it always used to. When I started paintballing, it wasnt uncommon to see a red dot site on peoples markers, and it worked in a similar way, where you had both eyes open (why you would shut one eye anyway, I dont know) but was alot more basic.
Whether it is all that useful is another thing, but regardless, it looks flippin cool! PE have nailed it with this one, looks really good imo.