When equipped simultaneously with other Augur set mods, a set bonus is activated; energy spent on abilities (up to +240%) is converted to shields. This effect stacks with Brief Respite for a total of +390%.
The set bonus does not have any effect on Inaros and Nidus since they do not have any shields to begin with.
The best way (it appears) to farm Augur Secrets is to play the lvl 30-50 Cetus Bounty. This requires Mastery Rank 3 or higher. The mission's 4th and 5th stage have a 2.08% and 4.76% chance of dropping respectively during Pool B (this refreshes every cycle or 2.5 hours.) If you do not see it in the lvl 30-50 Rare drop, you will want to wait for another cycle to attain this mod. Whilst it can drop from the Recon Commander, the drop chance of 0.5% is less than ideal.