I've played with several immersion systems in the past, and apart from the 3M one that was hideously expensive, the others tended to be a bit of a nightmare to clean up when you ultimately remove the rigs from the fluid - how does your system compare?  Is it more oily, or is it more on the engineered fluid side of the spectrum?  Do you have some solvent that is used to help remove excess fluid when removing a unit?

Also, how are you calculating the payback period?  It can't be the delta between the cost of just free-air systems and yours?  Plus I don't think the S9 is really the best ASIC to use in your pricing model.