I can see where a bend tester would be a good confidence builder for a novice. It provides validation that you don't get simply by examining the weld visually.
It would also be of value for someone who is practicing for their certs. It's not hard to read and understand the D1.1 section on evaluating welds to learn what defects are acceptable and what is not. Using that information for your own use is not the same as being a certified inspector. It's just one more tool that a learner can use to improve their work.
Dan