I picked one of these up the other day and can confirm it's legit.
CTEK MSX5.0 (5A) normally $190-$250 (Repco Link)
Currently available for $139 including accessories (Repco Link)
I don't think you'll get a better bargain than that for a CTEK, my M3 loves me for it because of the really low amperage maintenance mode.
For those wondering, 5A is fine for even a quite large vehicle battery.