Thou shalt remember to follow directions and proceed slowly.
I have been working with reloads from a automated progressive machine, and received on heck of a surprise in the form of half the cylinder and all of the top strap of a S&W 686 into my shooting glasses. This was a professional reloading company that supplied to OHP and many other agencies, not just some schmoe at the gun show. That said, when I had the time, I really prefer custom loads tailored to the firearm in question. Just be careful.