Osmocote is easier to find. Benefit of Polyon is that it releases its salts based on soil temps, not just moisture. I have trouble finding small jars of Osmocote with micros though. Polyon is sold thru suppliers to the commercial ag trade in 50 lb. bags. BWI in the states would be one such outfit but they will refer you to a local feed store, Walmart, nursery who they wholesale to.
Nutricote is one sold in stores, aka Dyamite sold at Home Depot.
The slow release should be all you need from start to finish. May have to tweak it once in a while. I get Ca from dolomite and my water source. Haven't used the Citrus FeED for cannabis but another grower is and doing fine with it.
UB