if you are going with a hq build, i would highly recommend going with the headquarters ignition system also - complete packages are usually far superior. i have a hq 113 build with the hq ignition and it works flawlessly so far.
i have an ist ignition in another big motor and it works well. it does not allow you to set the timing however, so if you want specific parameters, you do not have the ability to set them. basically the system takes over and you may sacrifice a small hp or tq number (if dyno'ed), but it does work well to reduce or eliminate pinging, etc. it is good supposedly if you change exhausts, air intake systems, or get a lesser quality tank of gas - it adjusts on its own to reduce possible detonation, pinging, etc.
in my particular build, i think it is retarding the timing a little too much and may be making the motor run a little hotter - not sure yet, but suspect i will try another programmable ignition just to see if there is a difference.
very advanced unit that probably works very well - again if you are not looking for extreme variations from the systems basic designed timing parameters.