Based on the HAMGEEK PortaPack H4M kit — guides apply to any PortaPack with Mayhem firmware.
Receiving is almost universally legal. Transmitting without a licence is not — and the threshold for prosecution is low when it comes to aviation, emergency services, or cellular frequencies.
Laws vary significantly by country. Before using this hardware beyond FM broadcast and other clearly public transmissions, look up the radio regulations for your jurisdiction. Key terms to search: radiocommunications act, spectrum monitoring, scanner laws + your country name.