What is a more formal way of saying "not worthwhile"?

Worth, worthy, useful, valuable, profitable, interesting, meaningful, praiseworthy, commendable, rewarding, desirable, laudable, advantageous, noteworthy, creditable, cost-effective, appropriate, notable, suitable, penalty, instrumental, purposeful, substantial.

The answer would be c. logical because it is explaining how the device is tempting which makes it logical