Oldognewtrick, yes we real painters never use a tray and I have never done the W. Been painting over 40 years never seen anyone do the W. Where the hxxl did that come from. Most likely from some makeover program on television I suspect. In the video above, the "howtopaintinfo' guy is a pretty good painter. I can tell just by watching him, although I do it slightly diffenet than he does ( https://www.youtube.com/user/InvinciblePainting/videos ) if anyone's interested. Trays in my professional opinion are an absolute wast of time if you're doing this for work. For the diy it's ok, JUST! They're cumbersome, difficult to work out of, don't hold much paint, difficult to move, easy to walk on, absolutely useless they are.
Had the earlier version of this. Sure, it was nice to keep moving without going back to the tray, but the extra weight of the handle - filled with paint, no less - and the hose (also filled with paint) made this heavy and tiresome to the arm. Also, cleanup was longer and a lot of paint was wasted in the hose.
I think the whole "W" thing is about getting the paint into the small imperfections in the wall. If a homeowner has done their owning taping and finishing, it might be necessary to change angles just to 'get it it in the grooves'.