Firemizer - any good?

I don't have a stove, just an open fireplace using coal.
There is always some partly burnt coal left to put on the next day's fire, so I wondered if it might burn more efficiently with this.

We have a multi fuel stove and only empty the ashes once a week . I find if the fire is on all day we don't need any more fuel after 5 pm as the heat has built up , so I don't see what this device will achieve

I have had a look at it, but I confess I have my doubts.

We have a wood burning stove. The wood burns very efficiently in it. If we burn it all day it will take three days before the quite small ashtray fills up with a very fine pale grey ash. This suggests to me that our stove is already burning fuel at maximum efficiency.

I think if your stove is not burning efficiently, ie lumps of charcoal and half burnt wood, or very dark ash in the ash tray that fills quickly, it would make more sense to speak to a sweep or the company the stove was bought from to see what adjustments need to be made to flue or controls before considering something like this