Can I just use public Wi-Fi instead?

We cannot vouch for the security of a network we do not run ourselves. The safer route is avoiding sensitive transactions on an unfamiliar open network, and turning on two-factor authentication in advance.

It depends on how much of the trip happens outside the accommodation. If you will be out walking, hailing rides, or using maps during the day, accommodation Wi-Fi alone is usually not enough.

This is a condition set by certain countries or venues themselves. If registration fails, the remaining option is to fall back on the eSIM's own signal for that stretch.

It depends on your actual usage habits. Try the data calculator on the site first to get an estimate, then choose a plan close to that estimate rather than guessing.

Some routes offer it, some do not, and signal quality varies a great deal by transport operator and route. We have no way of confirming this on behalf of any particular transport operator, so it is worth having the eSIM ready as a backup regardless.

Yes. Most phones connect to Wi-Fi and mobile data at the same time as a matter of course, generally preferring the Wi-Fi connection automatically whenever one is active.