The description is a bit vague, does the Ethopian tech Timkat from the Habesha alliance give a 10% hit point bonus to units and buildings PER monastery, or is it 10% even if there are multiple ones within range of each other? Sometimes there are two gold mines near the base and a 20% would make a big difference vs a rush, 10% is a bit meh for spending 500 influence.
It is an aura IIRC and same aura doesnt stack in the game as far as I can tell.
Think about it as getting an age 2 HP card for all units near a monastery.
Its not advisable to use it for rush situations, its definitely more a lategame option for when you want your units to never die on the frontline since the monastery also heals your units