GPS

On iOS, at least, I don't think it's necessary to disable location services and that may even prevent your phone from using your GPS. Bad Elf says:

When you connect to any Bad Elf GPS product, it immediately starts feeding location data to your iPhone/iPad/iPod touch. Any app that needs location information will automatically be fed the more accurate location data, in most cases, the location data provided by the Bad Elf GPS. If you are intent on forcing your app to use only the Bad Elf GPS location data, you can turn on “airplane mode to disable the internal GPS chip. But keep in mind that this is entirely unnecessary. In general, you should just connect to the Bad Elf GPS and the rest is automatic.

Note that airplane mode doesn't turn of GPS in iOS 8.3. Also note that there is apparently a bug in iOS 8.3 which causes problems with some third party GPS units. According to MacRumors, the latest beta of 8.4 fixes this.

"That was about PLBs, not general GPS devices."

With a normal GPS receiver, the whole problem is to get a weak signal received.

With a PLB, the whole problem is getting a strong signal transmitted.

Two completely different things.

–B.G.–

Thank you for posting this bit of information, I thought this might be the case, but wasn’t motivated enough to ‘google it’.

I have a bookmark for that. It’s an old article, so a few of the items have or may have changed (like no GPS in airplane mode – not a problem on my phone).

http://androgeoid.com/2010/09/why-use-an-external-bluetooth-gps-receiver-with-an-android-phone/

The 600 can have 5 custom maps on board at a time say from caltopo, very cool upgrade compared to my 62… as for other 24k maps go with the $30 subscription from garmin until you know what region you may want and go DVD then…