Yes, I use the 2 == $var
syntax. And yes, I have caught several typos over the years by doing so. YMMV.
As for how common the error is, my experience suggests that we tend to not have a good sense of the errors we make. A useful, painful, and humbling experience is to keep a log of every error of yours that you catch. Categorize them, then go back periodically to review them and think about how you could have prevented them up front.
Odds are that you will find you make a lot more mistakes than you think you do. And they will be of different kinds than you think. (Me, I make more "careless, stupid" errors than I care to admit.)