I haven't...but have read enough about them to know it makes sense, and I 100% believe the posted results I've seen from users. Sounds like it's kinda hard to get a BC these days...have read about people trying to contact the dude forever, with no results. It would be very easy to diy the same thing more or less...get a PID controller (lots of different ones out there, I'm partial to Auber) with relay contacts, a high temp thermocouple probe to mount in the exhaust/chimney somewhere, and just program it to only allow the exhaust temp to get to xxx temp before it opens the relay, which kills power to the combustion blower/damper...until the exhaust temp gets down to xxx temp, then the controller relay closes which powers the blower or damper again (assuming the boiler controls are still calling for heat) The temp differential you program into the PID is called the "hysteresis" I've done this very thing on my wood furnace(s) and it works very well. Not expensive either...maybe $100 total, or less. I have this one 1/16 DIN PID Temperature Controller (For Relay) [SYL-2342] - $42.98 : Auber Instruments, Inc., Temperature control solutions for home and industry They have helpful videos and their tech line is great too...they are pretty much a one stop shop for temp control projects like this. They are starting to have more options with Bluetooth/wifi too...pretty cool.
