From what I can understand (by reading) is this is a converter for AVCHD/H.264 to Pro Workflow programs like ProRes. What kind of advantages are there if I'm only using this to edit videos at a non-professional level? (In short, I'm not sure what are the advantages for using this program to run the footages through compared to just take the file and edit it not so heavily)
The reason we need a transcoder like 5DtoRGB or Canon's E1 plugin is because H.264 files off the Canon's CompactFlash card don't edit well in Final Cut Pro. Performance is sluggish because H.264 is a GOP format compressor (not all frames are stored in their entirety), and the system must rebuild the frames in realtime during scrubbing, etc. Codecs like ProRes store each frame individually, which dramatically speeds up editing performance.
Another reason to use the software is that 5DtoRGB allows you to select a custom decoding matrix, which can be created with its companion software dMatrix. In a nutshell, this lets you specify how the H.264 video is converted to ProRes, acting as sort of a first-pass color corrector. It's better to make these color decisions during transcoding, rather than transcoding and THEN doing your first-pass color correction. This, of course, is in addition to 5DtoRGB's already superior chroma reconstruction (currently better than almost every other converter out there).
Finally, 5DtoRGB can write timecode from the Canon THM files without requiring that the directory structure from the CompactFlash card be intact. This is a big time saver if you've just copied all your files into one directory.