So about efficiency I can tell the following things, battlehost can quite heavily change a battle, in our example my opponent fielded a fiefdoms army (yes a 2000points metal bar rangers fiefdoms army) against a fallen Realms host which I controlled.
The used battlehosts were: Swan Host, Mumak War Herd and Gorgoroth Horde, the Swan Host seems okay, can't sdpeak for the warherd since I took over the game after the other player left and my Mumaks were scatterered by Stampedes and the Gorgorot Orc Hord was simply amazing, wiping out 7comp Knights of Dol Amroth (including full command, Imrahil, in 2 formations), 2 more on foot (with Captain), and a company Axemen.
I lost the game as with 3 comp Orcs left, the last Swan Knight company just retreaded back and back which got me killed by the sole artillery piece in the game, a pity the one before me didn't use any magic of the Winged Nazgul, it might just have made the difference
I was thinking about including khamul in that host another time
anyway, those host make for great fun, but I think you can most assuredly still win without them