Ignition boxes - worth it for the effieciencies

I am looking at MSD ignition boxes and wanted to find out from people using the product what they think?

I do not expect any additional horse power gain. But the added efficiencies (burning fuel evenly and additional spark to the plugs) and associated benefits (little better gas mileage, cold starts and improved idle) do seem interesting

Beside the price – is it worth the install?

Any gotchas?