The thing about Ephemeron is that even if the Haste alone does not trade favorably with the STR Shikargar's stats in terms of gear allowed for TP (which is actually pretty realistic), to truly evaluate Ephemeron's worth is to determine how much more quickly on average Ephemeron's TP Drain effect lets you spam Weapon Skills. And I hear that Ephemeron's TP Drain is actually pretty potent.

(On a perhaps lesser note, the TP Drain does imply that you're depriving the mob of TP to some extent, which may or may not be valuable in and of itself, depending on the situation.)