At least they are being honest about there being a cost. A multi-provider SIM like that costs them around 70p/month, so the main cost should be collecting the charge. But they understandably do not say what their charges will be for their software services, but they are unlikely to be free.
My belief is that the product is under there years old so no-one knows the costs.
It is an interesting choice to use only a mobile signal - most places where an Ohme lead is likely to be used as anything other than a dumb lead have WiFi connections. I suspect that it is related to the evolution of the physical product from an existing pEVSE rather than being designed from scratch.
In terms of the costs I think that this is a universal issue for "Smart" EVSE after the OLEV grant period expires. There is a thread elsewhere where Rolec (as an example) got very evasive about future costs for the SaaS elements of their "Smart" product, and Kaluza likewise for their services which are used by a number of makes. Couple that with the nature of some of these "start-up" type companies in terms of long term survival and there may be some disappointment to come.
IoT is still the Wild West - some people do very well out of it but an awful lot get burnt. But in the long term a lot of good will come out of it. The difficulty in the shorter term is knowing which products to back with your investment, particularly if you only take a short term view of the benefits.