The valves arnt a total fix for the matrix failing, I;ve seen plenty go on cars even with the valves fitted, and some that are still going strong which have never had the valves.
My GTI had them removed before I got it, and I've had it for a year with nothing but lovely toasty warm heaters

Replacing the matrix isn't that hard really, its just lots of messing about. If you take your time and follow the instructions you'll get thru it no bother! If I was to do it again tho I'd take the dash out!