I got the Chimney balloon and to be honest, it all to often doesn't get put back after I've had a fire down.
I tried a similar Chimney 'cap' type thing some years ago, can't recall the exact name now, but it was installed outside on top of the chimney and there was a chain that hung down into the chimney which you pulled on to lower the cap.
It was installed fine and worked very well in terms of reducing heat loss and it was easy to release when I wanted to light a fire. Cleaning the chimney wasn't a problem either.
But the real problem came after a few days - the room stank to high heaven of a sooty chimney smell. I released up the chimney cap - smell gone in no time. Had chimney cleaned and lowered the cap again, within days not only the living room but the whole house had the same sooty smell.
In the end I had to have it taken out, credit where credit is due the company involved were excellent and gave me a full refund.