I'm only speaking from my own experience. Thats why I dumped it.
If you think that you have a box of cold water being pumped through the
heart of your fire most of the time it takes the heart of the fire
away.
perhaps if the room is small you may not notice too much.
I now have a lovely big wood burning stove and it heats quite a big
room comfortably even on the coldest day of winter.
Now if I had a box of cold water being pumped through it continuously I
would probably have lukewarm rads everywhere and a poor fire.
Of course there are variable factors like piling on firewood and adding
coal, stopping draughts etc but for consistency the wood fire without a
boiler is best by far.
Then Handy Mart would have to spend a lot of money putting in a new
cylinder with two loops and make the boiler. It would be a waste of a
lot of money and he would curse the day he put it in.