What tools do you use for measuring product-led growth?

If you're trying to measure the results of an experiment, assuming they're under a binomial distribution, you just need the numerator and denominator (people exposed to the experiment) for the control and treatment. Then just throw it into your favorite chi square significance calculator (I'm a big fan of the Evan Miller calculator).

In regards to other product tools, it's the same as usual. You can use Amplitude to look into user behavior. StatSig or Optimizely or all the other ones for running experiments. Really any out of the box feature flagging tool has experimentation capabilities.

As product led growth is a go-to-market strategy, the best tools to measure it is usually on the business impact, meaning revenue tracking and analytics tracking.