The documentation is lacking but the resonant rise guys have been doing a decent job of spotlighting some of the blocks available. Kirindave and corjaantje's videos inspired me to download mekanism, atomic science, ICBM and electric expansion. I installed them fairly hassle free on an existing map where I was fairly well established. Now I have barely scratched the surface of UE mods, all I have is a couple of windmills (brilliant models well done mekanism!) powering an MFR farm and an un automated insulation refiner. One of the mods also adds a circuit that isn't as annoying to craft as the IC2 circuits (they are second only to pistons for annoyance!). So far I am very happy to have installed them and can't wait to get further stuck in. I don't think I will get Calclavia's MFFS just yet because I have Minalien's version installed and I want to use that for now but I am very impressed with Calclavia's revamped version and I will do that on my next world I think. The only mod I am not sure about in the UE suite is Assembly Line but my info about that might be out of date.
In short, it doesn't hurt to try out these mods and even though the documentation isn't all there its fun to mess about with them. It might be good to do what I did and add the mods to packs you are already comfortable with so you don't get frustrated and have nothing to fall back on.