it depends... the quell system usually requires a large fire pump so if you have a small warehouse (for example 20,000 sq. ft.) it would be more cost effective to install in-rack sprinklers if the city water pressure is adequate.
If you have larger warehouse or need a fire pump regardless the quell system will be more cost effective.
Also, their are the maintenance costs if you eliminate the in-rack sprinklers since those never get hit by forklifts.
Contactors need to be licensed by Tyco to install the Quell system so not every sprinkler contractor is qualified.