Is this eSIM Scout plan valid for neighboring countries like Bosnia or Montenegro?

Negative. This specific eSIM Scout deployment is restricted to Croatia. Many explorers venture into nearby territories such as Bosnia (e.g., Mostar) or Montenegro (e.g., Kotor) for day trips. Be advised: these nations are outside the EU zone, and your connection will cease immediately upon crossing the border. For seamless connectivity in those regions, a distinct eSIM Scout plan would be required.