As a minor footnote, Airalo has a well deserved excellent reputation for quick and accurate Customer Service. I'd suggest you connect with them for questions about the Sim4Crew product. I'm contemplating that item for an upcoming European trip. They've always given me accurate, concise information via email.

Also, the S4C plans on their website include a +44 phone number and voice service for the rates you've seen I believe. Airalo is data only, so not really apples & apples comparison.