I mounted a 6 HP Tohatsu (who makes the same Nissan model) on my single CD22 a few years ago. Even though I haven't needed it to escape a dangerous situation, the peace of mind is well worth it, and it's been handy in a lot of ways. I also use it for trolling and general fishing, it's really easy to be fishing on the deck and use the kicker to reposition for the next drift.
Note that at 50% throttle I get the same speed of about 5 mph as I do at full throttle, so displacement speed is an important consideration. And this motor has been great... very reliable, and relatively light, which is also an important consideration on our boats. Due to the swim step on my port side I had to mount it on the starboard side, same as the helm, so when boating alone you'll get a list if the kicker is too heavy. Mine is very slight and I manage the fuel tank usage accordingly for balance, when possible.
As mentioned above, if relying on it as a get home engine it really should have a separate fuel supply. I chose to use the existing tanks, but if I was going offshore or in remote areas a lot I'd carry a small tank or add one (but where to install it?!). And yes, bad fuel is often the culprit with engine failure on the water. Then again, I do fill each tank at different times, and I only go to gas stations with newer holding tanks and quality gas.
Personally, I wouldn't go anywhere offshore without a backup. Good luck!