I've run MSD Digital 6, Jacobs Pro Street, and a stock mopar with chrome box in one of my drag cars and in one of my street cars. I can't say there was any appreciable difference in e.t., miles per hour, miles per gallon, cold start ability, or driveability between the three. Application was a naturally aspirated small block @ 11.5:1 squeeze running to 7000 rpm.
The mopar unit was nice because it was so basic yet worked great. Jacobs was neat because it was freaking huge and everyone just looked at it and scratched their heads wondering what it was. The MSD was nice because it had so much adjustability in it for rev limits and ignition retard.
Problem wise I never had any issues with the chrome box set up. I never had any issues with the Jacobs unit. The MSD, on the other hand, eventually had rev limit functions freak out in it. Set it to 7000 and it would only rev to 4000. Set it to 9000 and it would rev to 6000. Ihad to bypass the rev limiter completely to get it to work decent at upper rpm. I eventually pulled it out and it is still sitting in my garage. I suppose I could send it back to MSD and have them take a look at itt.
A few of hte guys I hang out with really like the Crane stuff as a good value, good spark, good options set up. Summit house brand stuff also has some impressive specs and pricing and I would probably buy either one of those ahead of an MSD again. I still ikethe Jacobs set up and with the addition of their nitrous controller, youd have a pretty complete set up.