Ah, good question. We use the term "Pre Release" sort of how Google uses the word "Beta." It's a fully functional copy, and it may be perfect. It may have some bugs we know about, but didn't want to hold up the release. Or, it may be fine as far as we know, but it hasn't been quality checked as much as we'd like.
There's nothing wrong with this copy of Vine's that I'm aware of -- but we just haven't completely given it the full testing we'd like to. We may issue updates to it, if we find issues with it, but you can use it now as it stands with no problem.