Old saves won't work. It tells you that on the OP. You should probably start a new game from a clean install as well.
The only problem with this is, like a ton of games where this happens, there's no mention of WHICH version this is necessary for. I've seen a bunch of games that put a message like that up on say, v0.3.4, and is still there on v0.8.6 or whatever. No mention if it's a constant 'restart with every update' or just an orphan notice that's months/versions out of date.
Unless people keep up to date with every single game they follow, and keep track of which version "you need to restart" messages first show up with, it's basically a useless message.
TLDR; I wish people who add "you need to restart/saves incompatible with new version" type messages, would mention the version number it applies to.
To be fair, unless it's a game with tons of choices and/or paths etc, I have no real issue with restarting once or twice (CTRL is your friend). I just like knowing that "Saves from v0.6 and before are incompatible with v0.7+" rather than having to guess, because I haven't been keeping track of each release.
No comment on the rest, I've yet to even download the new version.