simulations (assuming you get one in your starting hand, and 2 tower, with a water mark)
turn 1: play towers (+2 water), end turn, 3 net quanta producers (qp), have 5 water
turn 2: play khary, end turn, produces a tower (+1 water), 4 net qp, 5 total water
turn 3: khary generates a tower (+1 water), 5 net qp, 6+5 water = 11 total water
turn 4: generate a tower (+1 w), 6 net qp, 7+11 water = 18 total
turn 5: generate a tower (+1 w), 7 net qp, 8+18 = 26 total
turn 6: generate a tower (+1 w), 8 net qp, 9+26 = 37 total
turn 7: tower (+1w) 9 qps, 10+37=47
turn 8: tower (+1w) 10 qps, 11+47=58
turn 9: tower (+1w) 11 qps, 12+58=70
26 net quanta over 5 turns from 3 cards- essentially has paid for itself
70 net quanta over 9 turns, viable number of turns in a stall deck.
compared to having 3 towers in turn 1:
turn 1: play 3 towers, 4 total qp, 7 quanta
turn 2: 4+7=11
turn 3: 4+11=15
turn 4: 4+15=19
turn 5: 4+19=23
turn 6: 4+23=27
turn 7: 4+27=31
turn 8: 4+31=35
turn 9: 4+35=39
so at 9 turns 2 towers + 1 khary almost doubles the production of 3 towers.