My LFS has a few "remnant" cubes that he keeps for a "your choice $5", "your choice $10" etc...very cool. Little pieces of zoo and ric and what-not that he has fragged..
In good conditions, they do grow quickly. Zoos are probably the simplest to grow? May seem slow, but after 3 years of the same 55 gal, seems like lightening.
We got our first frags about 2 wks ago and I thought I lost them twice (literally couldn't find them) but they are obvious now.
I'd say try it.