They seem cheaper than anything else I have found and have the same one year warranty that the Hiblows have.
I am worried about running into the same issues you've had with stirring up sludge inside the tank. My septic tank does have at least one baffle wall ( I saw this the last time they were pumping. I do not have a proper access port to check it out myself), so I am assuming that as long as my aeration diffuser is not in the last chamber, not too many solids will be stirred up there and therefore shouldn't end up in my drain field.
Have you any way to determine if your metal hvac pipe contraption is really reducing the stir inside the tank?