The Echo is one of my favourite effect devices in Reason. Both the OVDR (overdrive) and TUBE settings are super useful for adding some analog grit to your sound. The TUBE setting creates a nice and strong EVEN 1st harmonic even when the Drive is at 0.
Check out my video below. You can see how I am not using any Drive on The Echo. I am feeding it a very hot input signal, using two Selig Gain devices. Notice how the peak level stays the same at -9 dB but the overall loudness perception increases when using The Echo. The OVDR setting is more transparent sounding than the TUBE setting which sounds a little more compressed.
UPDATE: You can now download the Combinator patch I have created for this example:
Input Drive (v1) (127.2 KiB, 1,444 hits)