I thought the same thing. Was surprised to see vodka so low. Biobellets are easier and less manual work, probably the reason they beat out vodka.
I'll take it a step further. I dosed vodka and mb7 for over 2 years. I was dosing a 4ml 2X/day for 8ml per day in 100gallon system. I feed heavy so some might require less. A fifth of vodka is 750 ml so I would need roughly 4 per year for around $30 per year. If you take the initial cost of the reactor out of the equation the yearly cost is about the same to replenish pellets. I am at 7 months and still do not have to add Ecobak pellets. I predict I will have to add approx 500ml per year for a cost of around $30. So really not that much of a cost difference and I don't have to dose it every day cause the reactor does the work for me. So far my params have been perfect so I don't think I will go back to vodka.