Normally I wouldn't drop a spoiler-filled page like this in a review but with Jay Garrick on the cover of the comic, there seems little point in avoiding it.
The Button concludes with little in the way of revelation for those readers who read DC Universe Rebirth. The biggest takeaway is that Jay Garrick - the first Flash - is trapped outside of time in the same way that the original Wally West was. The ending of the issue - and the ad for the next big event - also seem to confirm what astute readers guessed regarding who is responsible for changing The DC Universe... and possibly for creating it in the first place.
Where this is going is still anyone's guess but the JSA's disappearance also seems to be tied into a man who appears to be a ninety-year-old Johnny Thunder, desperately trying to summon his Thunderbolt. Then there's that blonde woman in Arhkahm Asylum (my money is on her being Saturn Girl) who keeps insisting that things are wrong and there's no future.
Thankfully, this issue is entertaining even if there's little development of the on-going saga. Joshua Williamson has an obvious love and knowledge of the characters involved and there's a great scene that sums up the difference between Bruce and Barry - despite similar training as detectives - and how they consider their shared experiences. The artwork by Howard Porter and Hi-Fi is similarly fantastic, with bright colors and smoothly-flowing action sequences. I also like how Porter's design for Jay Garrick resembles actor John Wesley Shipp.
Final Analysis: 9 out of 10. It's not shaking up the DC Universe or answering any questions but it's a solid comic with some great artwork and some neat character studies of The Flash and Batman.