There's a review of the Harmony on this site which can give you an idea of the strength of the IR signal, it seems adequate to me.

I haven't used the Pronto, but I can tell you the basic concept of the Harmony is unique. It treats your devices as components of an activity, e.g. Watching TV.

When you select an activity, the Harmony "knows" what you are currently doing (i.e. what states your devices are in), and accordingly turns off the ones not needed for an activity, turns on the ones needed, sets outputs, inputs, etc. as required.

E.g., if I'm watching TV, and select Watch DVD, the Harmony turns off my TV, turns on my DVD player and projector, lowers my screen, sets the correct sound on my receiver, and makes the buttons on the remote function for DVD activities (i.e. the channel up/down will now be fast forward, reverse, etc.).

This is all done with the press of one button. The Harmony knows what is on, how inputs are set, etc. There is also a Help button if things get out of sync. Pressing this, the remote asks about the state of the devices, and depending on your answers (yes or no), will send out the signals necessary to get things turned on correctly.

It's a very neat idea....