We were also on the this last August cruise with others that have already replied here.
The northern lights were only visible through our phone cameras. Otherwise they just looked like a haze in the sky.
It was also 2-3am their time so you will have to get up in the middle of the night to see them.
We also had private tours in Reykjavik for the 2 days we were there so we could see more at our pace.
We would not do a Disney shore excursion at Iceland now after doing our own, much better.
We were looking forward to Ísafjörður but still enjoyed our 2 days in Reykjavik.
As for which cruise to take, I personally would take the 10 night Iceland cruise as I believe it is more fascinating.
If you enjoy Iceland, you can always go back on your own so you can see more.
I would love to go back but if I don't, at least I made it there once.
Northern Lights:
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Can't remember the name of this waterfall. Could walk behind it!
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Godafoss Falls
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