Upgrading a Few iPhone 6s/6s+ to an iPhone 11.

I called Sprint to see what deals they have for trading in three iPhone 6s/iPhone6s+ (one 6s and two 6s+) since the devices have been paid off for some time now, we have been with Spring for 8+ years, and was told that if we purchased the new iPhone 11s over the phone it would cost $50 down for each phone and then $0 a month. This seems a little too good to be true! Is there something else going on? Does anyone know of any good deals with Sprint going on at this time that are as (seemingly) good as this or have anyone taken a deal similar to this one from Sprint?