They all have failures
If you use any electronic ignition, you will have eventual electronic failures. I have used MSD stuff for 25 years or better now and have had some bad boxes out of the package and some great for 10+ years. I do not believe that there is a known problem with any one box that MSD makes, but some can be damaged more easily than other models can. I will continue to use the 7AL3 on everything I run because I find them reliable and easy to trouble shoot in the field. I think that MSD is the best choice for Un Blown gasoline Drag Racing applications in my opinion.
As for what problems I have had, some miss fire at a given rpm, some stop firing altogether. For the most part they work or don't work or cause miss fire conditions. I have had two pro coils fail in 25 years and a few blaster coils fail as well.
Bruce