Where will board decisions actually be made?
Not where you'll register — where you and any co-directors will physically be when you decide things.
What it weighs, and what it can't.
The tool weighs the factors that decide this for most early-stage companies: where the board actually sits, expected profits, development spend, the EEA-resident director requirement, and where your customers are. It runs entirely in your browser and stores nothing.
What it can't weigh is the rest of your situation — where you want to live, what your investors have already told you they expect, whether you have a co-founder in another country, or what you've already committed to. Those routinely outweigh a few points of corporation tax.
It also can't settle tax residence, which is the question most likely to cost you money if you get it wrong. Residence can follow where a company is centrally managed and controlled rather than where it is registered, and that turns on facts a five-question form has no way of establishing.