The guide coat is very easy to use. It's pretty much just a tub of what looks like carbon black and a sponge applicator. You rub it on the panel and brush the excess off and away you go. You can get in everywhere with it. Doesn't make a huge mess, just a little extra dust.
I liked the idea that you just leave it sitting next to you and keep giving the panel a dust as you go. If I was using a regular rattle can for guide coat I probably wouldn't be checking as often. Highs and lows show up quite well with it.
It was a bit pricey at about $40 though but it'll probably last me forever.
I guess we'll see how good it worked when I get some paint on the panels.
Cheers