No one's mentioned it, but one of the most important considerations for tensiometers is repeatability, ----- the consistency of readings over several measurements.

This isn't too important if only using it to check for average tension of a finished wheel. Here, you'd take 3 or 4 sample measurements of different spokes, and individual errors will average out giving you a true picture.

However, if measuring each spoke during the build (as so many seem to do) good repeatibility is critical, otherwise you'll find yourself reacting to reading variances as often as to actual tension differences.