Yes. This splitter will work with any EV charger including Alfen.

In most cases this is not needed. It depends on what smart meter generation is in use and how much power is being used by both connected P1 devices.
Latest generation of the Smart Meters in EU, comply with the DSMR 5.0 standard, and allow to use up to 250 mA of current via smart meter's P1 port.

The main reason for that is that it uses powerful ARM Cortex 32-bit microprocessor.
It creates so to say two virtual smart meters inside, to be able to provide P1 data at the very moment the OSM needs it (without any delay). The other splitters cannot guarantee the immediate data delivery to both OSMs at the same time. In some cases such delay can reach up to 800 ms, which is too much for some brands of EV chargers.

The best solution is to extend number of outputs by connecting an additional regular active splitter to one of P1H-015 outputs.
It is important to make sure the EV charger is connected directly to P1H-015, not to the outputs of the additional splitter.

No. It does not support encrypted P1 data.