hello, i'm from belgium and i translate this text with google translate, so sorry for the mistakes.
Small question for you, where have you connected the power for the GPS and where have you gone with that block (5v adapter). I have a garmin zumo 395
There are different kinds of USB adaptors.
White is 1 amp
Black is 2 amp
Blue is 3 amp
I would recommend the 3 amp type for optimal performance of a phone or GPS unit.
Connect directly to your battery. Another option is to drill a hole and install a stock 12 socket from ebay and then use a USB adaptor which is easier to find.
If they have a screw collar, they will fit in a standard 2.8cm hole you put in your dash.
Ensure turned handlebars do not contact plug or wires even with protruding adaptor
Blue is recommended for smart phones.
I use my phone and Google Maps. If you download the map first on WIFI you do not need to use phone data with Google Maps.
I purchased a suction cup X Mount for my phone to use in the car and then a RAM MOUNT ball mount for the bike's handlebars to also use it on the bike. They are available everywhere and work great even on bumpy roads. If you have a helmet headset it will also transmit voice directions. With modern waterproof and shock proof cell phones, there is not any real advantage anymore in going with a dedicated GPS unit anymore, especially when you consider the large number of motorcycle software options available for an android phone.