A free replacement is not "free" as far as the accounting side goes. My guess is that there would be charges against revenue for the suggested retail price of the P & P Unit, the installtion fee and possibly a fee to remove and dispose of the older version DV.
For that matter, if they give away/install a unit for free (not a replacement), does that also become an accounting write off against revenue?
The idea of "free" valves for testing would be like, I don't know, high end matress sales, try it for 3 months, if you do not like it, send it back, no charge. If you like it, in three months, you pay for it.