Indiana wrote, >>Watch out for jet agitated units. There are alot of them on the market. You must have a mechanical agitator to use the hydro-seeder and not have problems with clogs and pump failure. <<
Don't make such broad statements. Turbo Turf units will mix as well as the mechanical units will. They might not with the really serious erosion control mulches from Conwed, but with normal paper mulch they will mix as fast as you can put it in the tank. The jet agitated ones that have problems use some sort of tube to disperse the jets into the tank through small holes. Turbo Turf, on their XPW series machines use 2" agitator jets and a HUGE bale buster that shoots in from the end of the tank.
I built a baby unit for myself, only 200 gallon, but I put 1 1'4" agitators, four of them, and a 2" bale buster. It will mix as fast as I can add mulch, by the time I get back with a bucket of seed the mulch is dispersed, dump in the seed and top off the tank and spray! Working alone, dragging my own hose and doing my own mixing I can put down right around 5,000 ft per hour. Not bad for a rig that I've only got about $2500 invested in.