Flytrex 3G is the best tracker, imho, but there's a huge backup right now on delivery.
I ordered 2 months ago, and still waiting for shipment.
That said.... They really are the best. It live streams the flight data (obtained directly via the P3 canbus) to Flyrex's servers.
Advantages to this over other trackers are:
1) Flytrex mobile app w/ live location. So when you're flying long range and you lose controller connection, rather than waiting a few moments/minutes in butt-clenching panic (or something of the sort), I just whip out my smartphone, which already has the Flytrex app up and logged in. "Oh, there she is, she's started RTH and is on her way back into range and the correct altitude and heading". Also works when flying full UAV/ground-station missions. Let's me keep an eye on progress outside of controller range. Updates every 500 ms, so those heartbeats let me know she's still in the air, and still flying correctly.
2) Post-crash analysis. What happened? Did we lose altitude first slowly? Spin out of control? Drop out of the sky? Fly away? etc... If you're over the water, or an area where it's not easily possible to recover the craft, you have a lot of data already streamed to the internet to do a post-crash analysis. Also a big deal if the craft goes down from serious altitude. If the force of the crash is quite severe, you might destroy or otherwise render inoperable the Marco Polo or other post-crash 2G/3G tracking device. With the Flytrex, I have the last known location up until total power failure. With any of the other trackers, you're waiting until after the "event" to get the appropriate data. The Flytrex has already streamed the data to the Internet along the way, and thus all data up to the crash is saved externally.
3) This is a bit less important, especially with the excellent logs the Phantom 3 and the controller record, but you get a nice auto-created flight route map and data log on the Flytrex website.
If you really really want to be safe, you could use a Marco Polo in conjunction with a Flytrex, but for me, if I only have to pick one, the Flytrex is the way to go for the most peace-of-mind per dollar spent.
The only major downside is you need to be flying in area with 3G connectivity. For me, that's not an issue, as 3G is prevalent pretty much anywhere I fly (and thanks to the Phantom normally operating at 200-600 ft AGL, it gets VERY good cell reception as it usually has better LoS to a cell tower than me on the ground). Unfortunately, the previous gen Flytrex 3G is only dual-band 3G, and hence locked to either U.S. region, or in the alternate model, Euro-region. Not sure about the new Flytrex 3G+ that's shipping for the I1 and P3, but I assume it has the same limitations. That's the same restriction for any 2G/3G tracker though, and hence, if you can afford both, a Marco Polo is a good backup.
Just my $0.02.
- Sam