Good thread, I'll add some thoughts if that's ok. After returning from a long knapping hiatus I had to decide whether to use my copper or abo tools. I was mostly an abo knapper before but used copper some, mostly to notch. While I have nothing against using copper I always felt more at home using hammerstones and antler. I've decided to go all abo indefinitely and put my copper tools aside. Currently I'm using a buffalo horn as an indirect punch thanks to Marty Reuter.
I think most copper knappers have an image that abo means crude or 'clunky', but that is perpetuated by limited experience in using abo tools. While copper and modern techniques such as FOG can produce artsy pieces easier (key word), those can be done w/ abo tools once mastered.
Again, I have nothing against using copper and may use it again someday, but being a 'studen't of abo techniques I want to immerse myself w/o distractions or temptations.