always a Gen 1 of any tech product will have its flaws. with new batteries being new tech, we never know what problems it might have. for example when tesla initially had their first version of battery in cars, i recall them catching fire with debris on road so they added titanium sleeve around battery pack to prevent it. i'm just concerned about new tech until it goes to mass production and they figure out the problems with it. same reason I didn't get Gen 1 Model Y.
there are some cons for DEMO vehicles. I was told by my SA that if it has any damages like chips on paint or curb rashes and other stuff they will not be fixed. however, they will fix issues like any broken pieces due to incorrect usage by test drivers like a loose or broken coat hanger. Previously people used to get thousands of dollars disc on demo when there isn't much demand. but with so high demand now on tesla's, you cant even get a dollar extra than what they advertised unless you are lucky.