I have an RAC Car Satnav.
I went out on my bike the week before last with the RAC Satnav on a PowerMonkey, in a plastic bag on a lanyard round my neck tucked in my jersey.
I could hear the lady's voice quite clearly and didn't make any wrong turns.
I adjusted it to 'Car Shortest' and NO motorways.
The combined battery life gave me well over the duration of an Audax 100.
Got some strange looks as I rode past Birmingham's open air market
I have a 100 Audax looming. I will be the one who shouts instructions with a North American female voice.