* Bonus points for tools whose authors have made the effort to explicitly compare it with competitor tools, particularly ones that acknowledge points where the competitor might have the advantage. ("Our new tech is better than existing old tech in every possible way" gets the side-eye from me; "Our new tech is better than existing old tech for these particular purposes, but old tech may still be more appropriate for these other purposes" goes a tremendous way towards confirming that the new tech has a real reason to exist.
* Is there documentation? Is it any good? This is a really low bar, but far too many new tools have no documentation at all ("just check out the source code") or have minimal, incomplete, or tautological docs ("bar.foo(): executes the foo method of bar"). A message board or IRC channel is nice, but not a substitute.
* How big is the API surface? Does it need to be that big? I tend to avoid tools where there are six different ways to do the same thing -- looking at you, Angular -- it suggests the developers are unfocused or in disagreement, and makes it harder to find support or documentation on any particular issue. Same thing if the API has undergone major breaking changes or paradigm shifts between versions (looking at you, Angular...)
* What does the tag look like on stackoverflow? This serves as a good indicator of whether the tech is too new or obscure to bother with, what the common pain points are, the average skill/knowledge level of its users, and whether help will be available if I get stuck when using it.
* Is there a relatively simple way to try it out? I'm much more likely to experiment with something where I can clone a repo and get going with simple but nontrivial example code; if I have to reconfigure half the settings on my machine just to get a hello world, I'm not going to bother.