I can't talk about spot lock but can highly recomend Dual Pro chargers. I've had a three bank Dual Pro charger since 2003, knock on wood here, with no issues whatsoever.
At their site Pro Charging Systems I didn't see my nine year old Three Bank model but things change.
“There is no difference between communism and socialism, except in the means of achieving the same ultimate end: communism proposes to enslave men by force, socialism—by vote. It is merely the difference between murder and suicide.” Ayn Rand