I have recently purchased the Garmin Zumo XT and agree that it is a very capable unit with simple controls and a very good screen. Two issues I had to address: 1) getting the Garmin voice directions to play through the RTL's speakers required a blue tooth adapter from LaMonster. The adapter allows both my cell phone Sirius music and the Garmin to play through the bike speakers. Also note that the Garmin speaker alone was not loud enough for my 75 year old ears. 2) Garmin will modify your route to a destination depending on how adventurous you want to get. But I selected the least adventurous setting and found that I was routed about 15 miles extra to a destination 50 miles away solely so that I stayed in interstates almost all the way. I am still learning what settings to use to get a good combination between shortest and quickest and least adventurous routes.
The easiest way for me to connect was to bluetooth the Garmin to my phone. Now when I'm riding I have my phone bluetoothed to the Spyder listening to music I can hear the Garmin prompts through the speakers via my phone connection.