Also, once the Meshtag service goes down or closes for good, all tags become impossible to read, which pretty much puts me off of using this for any permanent purposes. I suppose it will also have to deal with copyright infringement issues (and there would need to be a mechanism for submitting DMCA notices), but don't take my word for it. Related: it's easier to censor.
Whether these disadvantages are enough to make up for the fact that the codes can be drawn by hand, and can expire, only time can tell.
By the way, if this could be made to use squares instead of triangles, I guess it would be easier to draw on grid paper.