The conversion kit are just cards that have alternate info for the missions & objectives. All that info is in the rulebook itself so it is not truly necessary to have. It just makes it a little bit easier as you won't have to keep the rulebook out to reference is all.
That being said I have played it and it is fun, but I actually like both base games on their own more. ymmv.
That being said I have played it and it is fun, but I actually like both base games on their own more. ymmv.