Slow release has It's place. It mostly used in the turf and ornamental markets and some special ag applications. Question that you need to ask is What percentage of the nitrogen is s/r and of that percentage how many days does it release.
There are a bunch of different releases but the most common are 45 day, 90 day, 120, and ,180 day. They get more expensive as the days increase. A lot of your basic s/r grades you see will be made with a 45 day release polymer coated urea or something similar in a sulfur coated. These are not really giving you much more time than your other nitrogens would stay in the soil and available. Where they help are they help with N loss during that time. Kinda sorta comparible to a stabilizer