I have the Hypro Express end caps. I like them, they do let air out. They now have the option to be equipped with valves to drain them out. I had to buy those separately because they didn’t have the option when I bought the original end caps. How much are the Wilger ones? They look like a good deal just for flushing. But if the Express endcaps aren’t much more total investment (depending on how many you need), I’d get the Express endcaps. Another advantage of the Express endcaps is the don’t have the dead end space at the end of the boom/past the last nozzle body like any other end cap would have. The one thing about the express endcaps is they are more time consuming to install, and you need a special jig to drill the holes for them (it was a little over $100 when I put mine on.