Thank you for the feedback- its been a labour of love for me.

Regarding long-term feasibility: it's a good point and if it grows to the point of onerous costs I may consider introducing a paid tier for frequent travellers. TBH this is not a money-making pursuit for me and I've run other free/large-scale/fun apps for many years e.g. colornames.org

Mobile apps are certainly on the roadmap (although I hate building/maintaining them). At present you can install it as a Progressive Web App (PWA) and still receive many of the benefits (offline caching, push notifications, etc).

Cheers!