1) The website cannot call to external services, which is the primary reason why we thought about implementing it from scratch.

2) We want to invest in building a good framework to track such metrics systematically over time

3) We have some non-web API clients too. Adblock is not a problem.

4) Accuracy is better. Speed is not that critical and could even be a few minutes delayed.

5) The data will be kept for a few months at least, if not years. The storage costs are not a big problem. This is for enterprise based solution, where the deployment may happen in a private network.