Quote from Vilhamhmm, I was wondering about the upgrading too and whether it would break your projects.
I am so close to paying.
In my experience so far I've updated two editor versions and transferred my project between both. The only issue so far has been that a blueprint door with a timeline in it now throws up errors on load, which I can't find reference to online. The door works fine though, so I'm not sure if it's a massive issue. I tried re-making the timeline but the error persists. Annoyingly also you have to re-download any tutorial projects every time you upgrade, as they all change to work with the newest version, and some of these are 2-3gb.
All else seems ok, though my project isn't that complex yet. I'd say give it a go and buy a month's subscription, cancelling it straight away. It's pretty cheap and a month should include at least two different editor versions.