The problem is that Google is well-known for unceremoniously dumping stuff.
So my first question about any Google tool is: "Does it have enough non-Google people supporting it?" because, if it doesn't, it will die as soon as it becomes a political football.
My second question about any Google tool is: "Are there small projects using it and singing its praises?" Can I use the tool to do what I need to a handful of files after reading a couple of web pages for 15 minutes and have it work. I don't need to scale to 4 gazillion foobars--I do need to get stuff done without an IT staff of 100 people. From a cursory look, Bazel fails that question.
My final question about any tool is more personal: "Does it use C++?" because, if it does, then integrating with anything other than C++ is going to be a gigantic PITA. At this point there are plenty of fine alternatives to C++ that don't suck. If you don't have a clean, pleasant way of talking to things that only understand C library conventions, you fail and I'm moving on.