My experience with the Subaru "conditioner" has been very positive.
I bought a high mileage Westy with 2.1 about 9 years ago.
It had the classic wbx head crack near a spark plug and leaked out
coolant in small amounts with drops showing on the ground at times.
Though planning to replace the engine, I decided to add 2 small bottles
of the Subaru product to the main coolant tank.
My hope was only to delay the real fix until a more convenient time.
That engine has gone maybe 70k more miles since then.

Mark