"Just for the sake of trivia, note that the only interchangeable box/open end wrench between SAE and metric is that a 13 mm metric wrench will work on 1/2" SAE in a pinch ( 1 inch =25.4 mm) "

19mm = 3/4" as well.

If you are stranded, anything is better than nothing.
If you have no money or all the time in teh world, then open end wrenches are fine.

If you are making your living at wrenching, then the right tool will save you time (make you money) and in many instances save your knuckles. You may skin you knuckles when you work 6 hours on a saturday on your rod, but when you work 40 or more you can't afford to cut yourself up 6 or 7 times a week!

Broken tools don't work. Tools that don't work don't make you money. To spend $50 to $100 a WEEK on tools is about NORMAL for a working mechanic. Tax deductible too!

Hell, I spend at least $500 a year as it now, and it is just a hobby. Recently bought a 20 ton press, air nibblers, halogen work lights, and an assortment of odds and ends (scroll lock 3M pads, drill bits, etc)