powdering your own bark is a lot of work, yeah. The pieces cant be throw straight in the grinder/blender otherwise it will break it.. So you have to pre-break with your hands the mimosa first (bending the pieces with your hand and separating into thinner layers, and cutting up the layers into smaller pieces and then blending). This work can take hours depending on the quantity, and is quite tough on your hands. Then its also hard to get it really fine with the blender, normally it makes some powder, a lot of stringy material and some pieces here and there that didnt break. Lastly, there is the issue with the pink/purple dust flying around when you break/blend it, try to avoid breathing that.
Prepowdered is definitely easier but I think its also interesting to do the powdering at least once yourself. It gives a certain extra appreciation. And yeah you have to powder it before extracting or your yields will be very bad. Or at least pre-break them a bit and then make many days long acid soaks and/or go heavy on the lye on an STB and leave for long to help breaking up the bark. I definitely suggest powdering it, though, or buying prepowdered.