Been using Continental's tubular tire glue since I started riding tubs. One day I went to buy more glue from the LBS and they did not have any in stock. Searched around but only found Vittoria Mastik at another LBS. Figured I might as well try the Vittoria glue after seeing positive reviews in the forumon them.
Unfortunately, I found the Mastik a bit disappointing as it seems like it require much more of the stuff to get good coverage on the rims and proper adhesion on to the tire. I think the thinner viscosity of the Continental glue makes it easier to use/apply, so less mess. So if anyone here has been using Mastik and haven't tried Continental glue, I suggest you try it, as it could make tubular tire installation quicker and less messy for you.