My experiences with Osmocote have been quite successful being (as manofthetrees stated) it is in fact a slow release fertilizer. I typically use the general purpose (pink cap) so I cannot speak for the other varieties. I have also found off brand sold at Walmart for a few dollars cheaper and have used it. I cant tell you if it works better/worse, since I just found it this season, but it holds the same nutritional value as Osmocote.

We also use it at my nursery, although its not bonsai material, it goes to show it at least works.

I try and steer clear of miracle grow, in my opinion its like steroids for plants and as soon as the effects wear off you become worries that your plant is not doing well. It definitely has its place though, just be careful with it, or any liquid fertilizers for that matter, the effects can be overwhelming at times.

Hope my experiences help reinforce previous opinions and experiences.