From what i've seen in my area..... because the people who are doing the shake and bake here have no idea what they're doing, what is happening in the reaction vessel, no idea why they're using the chemicals they use, and don't wash the shit correctly...... it can't be very pure at all.
I have seen some people set up makeshift labs though that were yeilding crystals, chips...not big shards inches long but glass nonetheless. But they weren't using shake and bake.....they were using makeshift glassware. If i hear the meth was made shake and bake i've gotten to the point that i will not use it..... it has caused abcesses, and i worry about the fact that it probably has all the precursors in it. Scary. The only speed i'll even think about buying is from intelligent people who cook glass chips or the mexican glass shards.