I have a blue sky 6100 skylink using Cetus 100. The 6100 works well with some rough edges (firewall is non functional as an example). Certus 100 for
marine applications is limited to 25mb/month. Not sure what product they are trying to protect. We used it for
Atlantic crossing and 25mbytes was enough for twice daily
weather updates and frequent emails. You have to have a really tight leash on
ports to keep from burning through your data, not sure about WhatsApp and if the address and
ports it uses can be tightly controlled.