1. Pro, Pro Plus and Eco (NF+UV) - all these models have the same filtration stages.
2. Pro and Pro Plus have a capacity of 7.5L while Eco has a capacity of 5.5L
3. Eco is a more compact variant while Pro and Pro plus are slightly bigger. So, basically the dimensions are different. Depending upon the use case, you can choose whichever suits you.
Dimensions:
Eco: 30.5 cm * 20.5 cm *40.5 cm (w*d*h)
Pro & Pro Plus: 34.2 cm * 20.5 cm * 45.3 cm(w*d*h)
4. Pro plus additionally has self service mode which cleans the membrane regularly hence enhancing its life and consequently lower maintenance cost. Membrane is the most expensive filter in the machine and extending its life helps in keeping maintenance cost low. So, the overall maintenance cost should be ~3k for Pro Plus model while it should be around ~3-3.5k per annum for Pro/Eco models.