I used Icarus on a past trip to Europe and it worked very well, giving me a strong WiFi signal all the way to the limit of the 5.8GHz control signal (which is unaffected by Icarus).
I just got back from another trip to Europe, and this time Icarus did NOT work for me: I set it to 27dBm both on AC and RC, exactly like I did previously, but actual range got worse, with constant "weak signal" messages, even at short distances. I reverted back to stock and everything went back to normal, with both 2.4 and 5.8GHz signals giving up approx at the same time.