It should either by given the additional ability to grant you the keen-scout perk for free, or it should keep radar up while aimed with all of your weapons (except maybe snipers), not just your primary.
Minatosensei4's idea:
[quote]It needs the ability to keep radar up, regardless of the weapon type, and have enhanced radar like Keen Scout and Relentless Tracker. Perhaps the ability to highlight enemies with a red outline when ADS like the Signal MS5 Omolon sight.[/quote]
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Yep, mine sits in my vault 100% of the time. Tried it back in y1, wasn't worth the exotic slot back then and sure as hell isn't now.