Only if you bury them deeply and don't disturb the substrate, otherwise you could be asking for trouble. If you like to re-aquascape often and move swordplants, and the like, all around the tank then these would be a bad idea.
I have some large pond tabs in my non-CO2 tank. They contain urea, I have them about 3" deep in 4" of substrate. This tank gets very little replanting, and they have never presented a problem in the 6 months I've been using them.
Flourish tabs stay solid until completely dissolved, that's the nice thing about them. You can simply pull one up and push it back down as if it was brand new (just smaller). I've used jobes plant sticks in the past to see how they worked, they did a good job, I don't think using the fern sticks is any better or worse than the regular house plant sticks but you certainly don't want them to leech into the water, as Tom said they use urea as a nitrogen source. If you pull one out by mistake you'll have to siphon it out with a gravel vac as it becomes a slimy glob that's impossible to put back where it came from. If your substrate is deep enough and it's a slow growing tank you may do fine with them but I'd prefer Flourish tabs personally. Plus don't forget that jobes sticks contain NPK only, no other elements, while Flourish Tabs also contain a good array trace elements.