Anything which supposedly helps us play better while not actually working on the trumpet could be called a trick, but if it helps you, then it's really an exercise. It does different things from buzzing, so it's an additional exercise, not a replacement. Warburton sells a special device and also has videos on their web-site on how to use it, and the reviews they get are quite impressive. I'm thinking of getting one to see if it really helps me or if it is just another gimmick, so that I can know if it's something to add to my personal arsenal of trumpet playing exercises and something to suggest to students or not. The trick with the pencil exercise, as with all exercises, is to try it seriously and daily for a few weeks before making any decision as to whether it's helping you or not. If you don't see/feel/hear any difference in your playing after a few weeks, then it might not be something for you to pursue. Reinhardt makes a lot of it in his writings, as do people who approach trumpet playing from different perspectives, so there must be something in it which works for them. Try it and see -- I've never read/heard of it actually harming anybody's playing. So it'll either do nothing for your playing or it'll help, it seems.