Based on my experience with them, I'd strongly advise you to look at either a bow mount or transom mount option instead.

The motor mounted TMs have several drawbacks -

1.  They are not capable of operating in reverse, at least not even close to efficiently.  Forget trying to back troll, it's not going to happen.

2.  They tend to come out of the water and cavitate in any waves over 1-2 feet, this makes them largely useless unless conditions are calm or just a slight chop.

3.  You have to steer from the helm.  To some this is a real selling point, you can sit in the comfort of the driver's seat and steer.  The reality is, it severely limits your ability to control the boat.  The max. steering angle is drastically reducued, and steering input/boat response is slow, you can't react quickly to wave, wind, or structure changes.  Trying to maintain a course is next to impossible if you have one or more of those factors to deal with, you'll sit there cranking the wheel like a madman and still won't be able to put the boat where you want it.  On top of that, you put a lot of wear and tear on your steering system.

Unless you only fish in close to ideal conditions, and your fishing consists largely of straight line trolling, I'd avoid the engine mount trolling motors. 

Waxy