I had an opportunity to closely examine the Mulberry insert stove recently. Additionally I had a look at the new Mulberry fire-front made with a back-boiler in mind.
The Mulberry is distinguished by the "bay window" effect of having the firebox protrude from the front, this gives two effects, (1) It allows a much wider angle of view of the fire, but more importantly, (2) It exposes a larger area of stove to the room thus give more radiant and convected heat from this larger area.
One negative that comes to mind is the cost of replacing the glass. My guess it would cost perhaps as much as a fifth to a quarter of the cost of the stove.
The convection "box" of the Mulberry is in mild steel. This, in my opinion, offers three possible advantages, (1) It will not crack or damage easily on installation or handling, (2) The mild steel metal inner wall is thinner than a cast wall and therefore allows a larger area for better air flow within the chamber. (3) Mild steel is much smoother in finish and that surface on the inside the convection chamber will give better airflow with less drag.
Other features I noticed on the Mulberry insert are (1) The much longer slots, and (2) the additional side outlet outlet of the convection chamber. This would assist a better airflow from the convection channel.
In the above photo you can clearly see the air wash intake which is taken from the front of the door, and not from the convection channel as is the case in some stoves I have seen. Taking the air-wash air from the convection channel essentially robs some of the hot air and sends it up the chimney.
Another detail you can see is that the door handle latching point is quite a smallish cut into the convection channel wall, and therefore less likely to cause any disturbance to the air flow pattern.
All of the above said, I have not as yet observed the Mulberry insert in operation, nor have I spoken to users and got their views. Speaking to one retailer, the feedback seems to be positive with a much more satisfactory heat output than some other inserts.
A Look at the Mulberry "Fireplace Door"
I had a quick look at the Mulberry fire front or fireplace door. It is constructed from the same castings as the insert stove, with just the firebox and the convection box removed.
It also has a drop-down fire grate and a large square-shaped baffle. The price though is VERY expensive for what is essentially a cut-down stove.