In my state there are rural areas where long duration voltage swells and sags are common. Buck – Boost transformers are useful only if it is auto regulated. Fixed tap buck-boost transformers can destroy the load equipment which is normally lighting load or a motor. But adding regulation is extra cost and also greater maintenance. Even if cost is tolerated maintenance is difficult in rural areas and the voltage correcting transformers gets bypassed. So I am not a fan of buck-boost transformers. I would prefer a charger – battery – inverter combination for small loads and a motor designed to tolerate a wider voltage variation.