Don't know about the two you mention but I went through the "which aux" thought process recently and settled on a Suzuki DF6 which then became a Johnson 6hp (same engine both made by Suzuki) due to the Zook being unavailable at the time of ordering.
Reasons why:
1. the dealer I got it from quoted a good export price relative to the prices I'd seen on the web and it was right at the bottom of the price range you quoted
though that was ex VAT as it was being exported
2. the 4, 5 and 6hp Johnzuki engines are actually the same engine with a different carb so the 6 is the same size & weight as the 4 (26kg I think)
3. I wanted something Japanese with boring reliability that will start on the first pull when required, and if its been running the same day it will start on the first pull every time. From my limited experience if it has not been run for a week or so it seems to need about half a dozen pulls which is still pretty good
4. it has an internal tank and a feed for an external tank
5. I wanted a 4 stroke so I didn't have to mess around with stale 2 stroke fuel when the main fan stops and could just use fuel out of my cans for the main engine if required
If I did it again I'd probably wait for the Zook as its black so easier to keep clean but apart from that I'm pleased with it
Info on it
here and
here
This may not of course be the right choice, and it may not be the best engine, but it seemed like the right one for me and ticked all the boxes for my needs so worth a look
HTH
