I was lucky enough to find out that my neighbor had purchased a Magnetospeed V3 with the XFR and the rail mount (about $450 out of pocket). I found out because he needed the "friends and neighbors" IT support
The device was easy enough to use and not really all that complex to get attached and aligned properly. You can see all those reviews on Youtube.
His problem was the XFR. It wasn't working well with his Android devices and that's how it came to me!!!
I first tried it with my iPhone and it worked well. The app from iTunes was easy to install and use. It connected well and reliably.
However, the android devices were indeed an issue. I noticed the PlayStore app was beta. I tried it on a handful of devices and it was pretty random on connecting and communicating. NONE of the devices I tried were on the very limited "approved list" on the MagnetoSpeed FAQ. For me, that's a deal breaker because I'm not inclined to take an expensive tablet just to support this device when there are sub $100 android devices that should work for this simple app.
I called magnetospeed and had some very nice conversations about why they used an analog interface instead of Bluetooth, blah, blah, blah and when would the Android app be updated from Beta. Unfortunately, there are no plans right now
I then focused on the XFR app itself. Not really a lot of "must have" features to tell you the truth. Since the microSD card has all the data, it's really easy to transfer the CSV to a PC and use excel to graph things and manipulate data. I'll be happy to send my very basic XLSX template I created for my friend to anyone who'd like it. The data in the attached example is simulated from the XFR app on the iPhone. I have NOT thoroughly evaluated/debugged my spreadsheet
Given the XFR seems to only work with a very limited number of higher end IOS/Android devices, given the functionality of those apps vary some, and given they're a bit basic, I'd find it hard to recommend the $25 XFR at this time.
Don't take that as a slam on the Magnetospeed. It seems to be pretty solid and I like not having to set up a chrony!!! I hope to get more time with his magnetospeed as I decide on it or the labradar. May make the labradar more attractive to ME as we'll have both devices at our disposal!!!