FWIW - I bought a 10" f/5.6 Coulter mirror 10 years ago and the figure was smooth but it was grossly under corrected (only about 1/2 corrected). Unfortunately, at the time I didn't think to test it, I was too excited about getting such a large (?) mirror. I have since refigured it and it performs well.
The diagonal that came with it also appears to be less than wonderful. Take these comments with the usual grain of salt, these optics were purchased during the Halley hysteria (the manufacturers, not mine) and thus are probably not typical of their current product.
................. Steve