Bridge Rectification

More C&H. The motor crew was testing DC motors using an AC variable
transformer and a little half-ice-cube sized "bridge rectifier" with
four lugs--2 in and 2 out. Cost was two or three bucks and the
counterman claimed, "Ya can pull 40 amps thru these things."

Is this a reasonable setup for motor testing, and one unlikely to
release magic smoke? By reasonable, I mean is power of this quality
similar enough to that of a "real" power supply as to render
meaningful tests?

Heck, I happen to have a variable transformer and for three
dollars ...

Thanks.

--Jack