I think it is important to understand what the long term requirement is. I use a Cerbo GX on my boat with my Quattro as it allows remote access via the VRM with full configuration of my kit. It also shows the level of my fresh water tank, both fuel tank levels, voltages of the various batteries on board as well as monitoring the temperature and humidity in the cabins using Ruuvi devices.
It also interfaces with the NMEA 2000 network used by other equipment on the boat.
I also use Node-Red running on the Cerbo to monitor and switch on kit remotely, i.e dehumidifier, or to start to charge the starter batteries when we have sufficient solar power spare.
So for me the expense of a Cerbo GX justified itself.
For a simple MP 2 type installation, with no ‘extras’ the cost of the MK3 should be regarded as one of the parts you need to purchase, just like fuses, required to install the inverter / charger.
At home I use a RPI3, so I do have a MK3 to connect it to my MP 2. I had a RPI, with a CAN bus HAT for the battery, spare so used it, otherwise I would have bought a Cerbo, alongside the cost of MP2, battery, MPPT chargers and extra PV panels for this project the cost of the MK3 was insignificant.