That's it in a nutshell. When I use it I prefer to heat the parts before application not after, probably to the same end.
Oxpho is pretty good stuff IMO. Not a substitute for "real" bluing, but pretty good nonetheless. If in doubt, follow the "destructions" on the bottle.
On a dare, I actually blued an entire rifle once with the stuff. It was on a Winchester M67 I was refurbishing for a friend. I hand polished the entire thing, to 400x, just as if I was going to rust blue it. I then used Oxpho over the entire thing. It turned out very nice- looking much like the original Winchester blue from the 40's. Five years on, after much use/abuse by the kid it was gifted to, it looks as good as it did when done. I'm not advocating Oxpho as a panacea, because in truth it didn't save a lot of time on that project- the hand polishing is the same regardless of coloring used.