Probably one of the few that will say not to use them, or very sparingly.
In a water environment there is little stopping them from "releasing" fairly rapidly..
They make ones specifically for water environments but NOT available in the US..
bottom line is, not much different than water column dosing..
I've gone to the extreme in using osmocote and I'd generally give it a thumbsup, especially if you use it properly. Like @jeffkrol
said it can release fairly rapidly into the water column if it's exposed to free water.
I once used a 1 pellet deep 26x26cm layer on the bottom of a 30x30cm tank of mine that grew a massive Cryptocoryne parva carpet. I capped the osmocote w/ about 2 inches of the black aquarium sand sold at Petco. They lasted about 2 years without having to do much additional fertilization (aside from CO2 injection). I remember having a massive algae bloom (green water) at some point during the earlier stage of the tank, which I assume is from the rapid release of nutrients. I also grew a colony of RCS in that tank that that did really well.
I have also used osmocote by filling Laguna plant spikes and inserting that into the substrate. Would really only recommend this if you can bury it deep enough (burying at an angle works decently well). I did this in my larger tanks (60gal and 75 gal) and had pretty good results.
Nowadays, I primarily use it to power grow plants that I sell on the forums. I stuff like 5 or 6 pellets into a 1.5x1.5" rockwool cube stuffed into a 1.25" net slit pot. I only recently had an algae bloom (which I'm attributing to this) because the plants in two of the pots melted and basically released all the osmocote into the water column through the channels that previously contained the plant stems.
Overall, I'd say it's a good, economical choice for substrate dosing. I wouldn't consider it a true alternative to water column dosing though, since my understanding is that some plants are preferential substrate feeders and others can benefit greatly from both substrate and water column fertilization (probably varies from species to species). I personally do both, and lean more towards substrate dosing when I'm growing crypts and erios, though I will say FME rotalas and hygros tend to do really well with both root and substrate fertilization.