I have a Merc 9.9 pro kicker 4-Stroke on my Starcraft 196 Fishmaster. Its a great engine (its a long shank), hardly burns any fuel and easy to control (I have a separate throttle up front). The one caveat is to avoid ethanol gas or if you use ethanol gas disconnect the fule line on the way in and burn it clean or drain carbureter (remove drain screw a then replace after draining (Recommended and easy to do). Due to EPA requirements it has small orifices and jets that can get clogged if ehtanol gas (even if treated) is left in the carb. I'm sure this is the case with many of the newer model small engines.
I have the kicker and the 4 stroke main engine on the same steering cable and they both run off the same gas tank. Its a good way to go.