Can't help you there Joe I've never heard of BLF BFO model, especially operating at 10 kHz.
Most of my BFO operate at much higher frequencies, 288 KHz on most Garrett and one rare Garrett at 455 khz. May be the last surviving 455 khz model, Garrett only made around 12 units then recalled them changing the kHz back to normal. Allan Cannon purchased one when he worked for Garrett but decited to keep it, glad he did he passed the unit over to me a few years ago.
Even the coils are special made for this rare model, and only work with the Garrett 455 khz BFO. If memory serves me right, I think Allan mentioned Garrett didn't pursue with 455 khz because it was too sensitivite. I Auctally like the extra sensitivity, plus it's probably the last surviving 455 khz BFO Garrett made.
It is by far my most sensitive BFO, Will pick up a tiny nugget that's how sensitive it is. In fact, Was using it this morning at a local school. I think the higher kHz makes BFO more sensitive, that's what I'm noticing. Have other brands, Whites and several others but Allen Cannon's old Garrett Coin Hunter 455 khz is extremely sensitive.
Good luck and hope you find more information on the BLF BFO model.
Paul