As for now my plants are doing fine.
I have divided them in two batch; the first one went in my unheated greenhouse, the second one indoor in a sunny unheated room.
Both have been doing really well since the fall.
The ones in the greenhouse have experienced a pretty long lasting cold spell (we got minimum temperature in the low 20s °F for about 10 days) so, even if i didn’t measure the temps in the greenhouse, i did expect them to have experienced regularly temps of about 34°F every night for more than a week. They didn't show any damage: only true difference from those in the warmer indoor room has been the leaf color, that turned to a nice copper/red for the plants in the greenhouse, and remained of a solid green for the plants indoor.
Can't say that this plant doesn't look promising.