It's useless, since our engines are aluminum. put a magnet to a piece of aluminum and see what happens. It will not stick.
Therefore: magnetic drain plug + aluminum engine = useless mod.
The internals of the engine won't affect the motor like you may think.
They will not be a cause of metal shavings or deposits in your engine or oil or Oil Filter
. That just won't happen ever.
If you are worried about any deposits in the engine just get an engine flush. Toyota will do it for $100.
With the tranmission, I have never heard of any one using a magnetic drain plug for that and the reasons are obvious.