WAGO221-612 Lever-Nuts 10AWG 2 Conductor Compact Wire Connectors 10 PK

Is the 221 series rated for aluminum?

box above shows ul listed, etc, but then says "do not work.inder load!". at some point the power(load) has to be turned on, so what does that mean?

Can i use these on 12-2 wire?

Is there a trick to opening the tabs? Mine will not open at all.