I just did some quick benchmarks of mbarcode versus a pure Qt app with only one button. The approximate results for boot times are as follows:

pure qt app: 1.9 s
mbarcode (lens cover closed): 5.4 s
mbarcode (lens cover open): 9.2 s

There's nothing scientific here, just me starting the application from terminal and running a stopwatch a couple of times. The numbers are an approximate mean value.

In other words. It takes almost ten seconds to start scanning, and over 5 seconds before the user sees any activity. This should be lowered significantly. I'm going to look for some possible enhancements now.