I have m105, UC, xmt360 and red mouse glaze. I find that UC is a great 1 step for most paints. If I have a one step correction I do a test spot with xmt360 and UC. Then I look at the results. if xmt360 makes the paint look good, then i save 15mins. if xmt360 doesn't have enough correction then UC and wax. if its just xmt, then i buff off and i'm done.
xmt seems to give a month of protection. maybe 2 if garaged. any product that claims to be an "all in one" really means it doesn't do any one thing really good.
1 step corrections are for daily drivers that want their car to be shinny for almost no money. UC is better at removing oxidation than xmt360 and any polish. It will make the car shine alot more. If the car is white or silver you won't ever see any marring. If its black, then use a polish or all in one product, but preferable do a 2 step. explain this to your client.
for me one step details tend to take 4-6hours, including wax and the interior.
I remember an old meg's commercial that says UC doesn't need to be polished. SMAT tech really works.
[ame=http://www.youtube.com/watch?v=PRokMbzUcoc]Meguiar's Ultimate Compound - YouTube[/video]