Transmission Fluid Flush in DFW Area

Looking to get my tranny fluid flushed soon. Toyota of Dallas is offering the service for $279.95 and says it includes 12 quarts of Toyota premium tranny fluid and ZAK premium transmission additive.

My question is is this a good deal and why are they putting an additive in the fluid?

I would do it myself but I am out of the doing my own service game in the driveway.

TIA

 

When I had tranny issues, they told me the transmissions are non serviceable. That's why when you get your fluids checked and so on they don't look at your tranny, (the reason my went dry). I wrote the 300 of as a fair deal since they had to drop the tranny and so on. Or that's what they said. Didn't make a difference in the long run because I had to just get a new tranny.