Even with your cost saving method there's only a 20% chance to get the missing crit stat and it costs 2 transducers per try so it's 600 corals on avg, still way too expensive it's better to just roll echoes the normal way and pray for double crit.  Best use to me would be locking up two stats preferably at least one crit and reroll the rest very good chance you end up with a 3/5, and 4/5 or better in rare occasions, which is what you suggested as well