Primary differences: RM Complete releases nutrients slower, designed for an aquatic atmosphere. Osmocote is designed as a terrestrial product and as such when subjected to full submersion can leach pretty quick. YOu need to make sure you bury osmocote as deep as possible.
RootMedic Gel Caps are a thicker, tougher product than I've seen offered by others. The capsules take about 40 hours to dissolve in the substrate, so you can get them in and don't risk them falling apart before you get them to the dirt. I've worked with about every gel cap out there and these are the best i've found. They also add a touch of potassium to the mix, not much. But some.
BTW, at room temp, with any atmospheric humidity above 20%, osmocote begins to leach nutrients out of the membrane and will slowly but surely have as much outside as they do inside. Their membrane reacts very quickly with water in any form. SO if you buy a bunch of it, you'd best store it tight and use silica packs to go with it and keep them dry.
I use the same nutrient content as Osmocote+ because it works. Well. Why mess with that? The other products I offer allow all kinds of opportunities for customization.