I bought the GNS 5870 MFI GPS Bt Receiver "WAAS" Enabled for use on a month long trip abroad in Asia, hoping to use it with both an iPad (no GPS) as well as iPhone for better reception while traveling, for navigation, GPS geotagging, and trip logging.

Why I chose this unit over the competition:

Bad Elf GPS was the only other option at the time, which meant that I would have to physically connect it with my Apple iDevices making a lot of my other plug-in portable battery extenders moot, as well as the worry about physically damaging ports or the devices.

At the time of my order, GNS 5870 said that it became "WAAS" enabled meaning they may have increased the accuracy - bigger plus than using just my iPhone's GPS chip.

German engineering! I love German products.

In use:

I started having problems two days (into my trip) abroad. Sometimes it would refuse to turn on. No, this isn't a case of not knowing how to turn it on or turn it off - I had to reset the unit in order to get it back on.

OK, so a reset got it working for the next week or so.

During the week it worked, I had some issue with it turning on too easily (which was OK since I was logging over 10 hours a day). Battery life was excellent. Here's what I took issue with: the surface of the unit started looking really beat up.

The above is what the surface looked like after keeping it in safely tucked in my mesh backpack after two weeks.

The rubber suction mount is simple and works well. I used it a few times on the high speed bullet train in Taiwan and it held the unit securely.

Week three and four, it just wasn't working. Sometimes it wouldn't power on and have to be reset, and other times it just wouldn't lock on. Well some of the time, it would not report a lock (as reported by LED status lights) but yet still provided a decent signal to the iPhone. And sometimes it wouldn't provide a GPS lock, until it was connected to the iPhone via bluetooth. Strange behavior!

Finally at the very end, it stayed locked on (reported its location) at this one train station in Chia-yi, Taiwan. It never budged from that spot, no matter how many resets I performed nor how ever hundreds or thousands of miles I've traveled. Turning it on, connecting it via bluetooth always reported that one train station.

The unit turned out to be a total failure for me. I ended up having to rely on my built-in GPS chip on the iPhone 4 the rest of the way - and without the full aGPS assistance so connectivity was slow.

So since I was abroad, I could not process a return to amazon.com. I contacted customer service and they allowed this one exception for me to return past the 30 days. Unfortunately, due to the way the unit looked after two weeks, and because they could not process it as a replacement, Amazon only gave me just over 70% of the purchase price back. (statement corrected, used to be 50%).

Yes, I'm bitter about this. I cannot recommend the GNS 5870 based on my 5 week experience with it. Go for the Bad Elf GPS Receiver for iPod touch, iPhone, iPad (66-channel, SBAS/WAAS, 10Hz) instead.