An AP installed in the cockpit is subject to all kinds of unintended consequences. One below deck can be installed to guard against such events. More robust is better than marginal. Power consumption is important, but can be provided from non-engine sources. You will use the most power in the worst conditions, where you might be using the engine anyway. Reliability and backup is very important. Look at the "spares package" if the mfgr recommends one, which they should. And most importantly, install it early enough that you can fully train yourself in all of its operations and capabilities and sea test the installation.
My experience comes mostly from military electronics and some from sailing, none from crossing the Atlantic.