Great writeup here but I have a question on whether Product Analytics is at all appropriate for Startups. I'm incredibly biased (this problem is why I built Chartio), but I think these tools end up being quite bulky, expensive and a non-agile way to do analytics on your product. I feel these products are best suited for later stage companies trying with great tracking detail to improve a funnel or engagement metric, not simply monitor usage.

The majority of the important things for a startup are usually already being tracked with timestamps in the database (new signups, new users, churned users, new todo items, etc). If a key metric is not directly tracked, there's usually a good enough proxy available somewhere in the database. A Busineess Intelligence product, or a SQL to chart tool is much more applicable and affordable in the startup stage.

There are likely going to be responses here "But what about..." and I'll premptively respond to those with the question: Could that be answered/solved almost just as well with a query to the database, without sacrificing the agility, extra setup and data collection time, and expense overhead? Those are all very costly things for a startup.