Easy 3in1 and Unique 3in1 system

Could you explain Easy 3in1 and Unique 3in1 system as I don’t quite understand it?

Yes, some Novatec hubs are supporting these two systems mentioned by you. Both systems are related to cassette body exchanging/swapping so we’re talking about rear hubs only. In catalogues they are being marked like this:

Easy vs Unique 3in1.png

Unique 3in1:

This system was designated for Novatec wheels and it says in general that changing the cassette body between Shimano, Campagnolo and SRAM XD is very simple, without need of any additional parts (washers, side caps). You just uninstall Shimano and install Campy for instance, keeping the same side caps, without replacing or relocating anything from the hub, just a simple swap of cassette bodies. Examples of such hubs are: D412CB, XD612SB and XD642SB.

Easy 3in1:

This system also deals with cassette body swapping, however hubs supporting this system require relocating the washer from one side of hub to another (for example from the left to the right side when changing from Shim to Campy). It means that all parts required for cassette body exchange are already there, as part of the hub, you just need to relocate the washer. Even the side caps remain the same, no need to get different ones. Examples of such hubs are: FS522SB, F172SB or F482SB etc.
PDF instruction file in Documents section below clearly explains swapping from Shim to Campy for hub F372SB so please check it out for better understanding. There is also a video instruction below on this topic for hub model D482SB-SL so don’t miss it out.    

Please note that rear hubs not supporting any of two mentioned systems will require a different side cap or even an additional washer when changing from one type of cassette body to another (Shim to Campy for instance). This is important to know when changing your cassette body so that you can make sure you have all the needed parts for swapping your freewheel body.