Did the OP check the specs on his intended purchase as to the autoformer's disconnect voltage level? Because most autoformers will boost good voltage to perfect level but simply disconnect low voltage.
I routinely run 150 ft of 10ga on a 30a connection. At the upper end of the power draw you can definitely see voltage sag below 105v. This is exactly the voltage you want boosted but most autoformers simply shut down and declare the job done.
I personally have no issue running an air conditioner all day on 104v and I don't care who knows it. But buying a $500 autoformer to protect a $600 AC from premature aging is just silly (IMO).
A cheaper and more effective solution would be to upgrade the 30a wiring to 8 awg. Same plugs, but no more voltage drop at 30a X150 ft.