1) This is an informal shorthand agreed between people who already know each other in the particular context of work, so there is no surprise or ambiguity. Outside this context, I would use, and expect to see the dictionary sign.
2) It functions as an 'in-group' slang, boosting cohesion and good will.
3) There is a certain humorousness in bending a symbol into an informal use. This is more pronounced in cases where the alternate meaning is irreverent or vulgar. I have no intention of expanding on the second point.
4) One does not have to be facing the SL speaker. The 't' symbol can be recognized from beside the person or even behind. Point 5 gives the rationale for this.
5) It can be communicated without changing focus or posture, allowing concentration on the task at hand without breaking the workflow.
6) Though 'thanks' is a brief gesture, 't' can be signed and understood even more quickly. Just a flash of meaning.
7) The sign for 'good', while it is also used to communicate thanks and has advantages 4,5,6 listed above, can be ambiguous, violating the principle of least surprise (see point 1 above). It is more generic, while 't' is specific.
However, I think it's fair to say that a rudimentary system like this one is scripted, and is not tuned to the informal and complicated contexts you describe. You can argue that it's fair game to pre-program the device to emit "Lemelson" for #L, just as you might prepare an interpreter with proper nouns before a gig, but I think it goes against the spirit of the claims made in the video.