I need some advice on whether to get a 1 room or multi room heat transfer kit.

We've just had a new fireplace installed and its going great. We're now in a position where we'd like to distribute some of the warm air to the rest of the house. After some research I have settled on the Heat Trans brand from Bunnings, but am unsure whether to go with a 1 room or multi room kit. Ideally I'd like to go for a full heat recovery ventilation system but at this stage the cost is prohibitive compared with the cost of a heat transfer kit.

All three bedroom are at one end of the house (see floor plan below) and the doors for each room open on to the hallway very near each other, with this in mind the fireplace installer suggested we go with a one room transfer kit that comes out at the bedroom end of the hallway rather than a multi room kit into each of the bedrooms. The theory being that the extra ducting used in the larger multi room kits would lead to greater heat loss (1/3 degree per metre is my understanding).

Can anyone fault this logic?