I guess it depends on your situation. If you get lucky with caving 120 silver isn't that much.
But it is just as easy to gather some wood and put it in a chest and forget about it for a while. Sure it's not free, but w/e.
It's redundant to discuss here tho, if you want low but free mj FZ is ok, but not really anything for bigger needs.
120 silver is not that much. i usually have about that much by the end of my second resource gathering run. my first run is always designed to get the smeltery and t2 tool table for TiC. this means that while i could use wood/charcoal as my first base power setup, I'd be out of position to have it automatically feed itself trough farms. everything before this uses the smeltery for ore doubling, so everything is still manual at this point. (manually making several stacks worth of charcoal is something i prefer to avoid. it's tedious)
This solar setup is enough to kick start an MFR treefarm for instance. but until such a farm is up and running i put a big premium for charcoal. strip mining with a hammer uses a LOT of torches. now getting a boiler requires fire charges, and unless you find thaumcraft flowers in the desert. (not likely in a bop heavy world) you need to go to the nether. with the nether being so much more dangerous now than before, it's better to use an alternative to the RC boilers until you have good armor.
This invention definately have it's place imho.
besides. it is good for low levels of intermittent power in all plications where there is no need to keep lots of energy reserve. like running a wheat farm or similar non energy intensive autofarming.