Perfect when you're doing initial prototyping, or if doing a project with teensy and you don't need that teensy form factor. Board works as advertised, although I've only used it with 1 of its configurations. The assembly can be a bit tricky - time and patience is your friend. If you have questions, support is there to help you thru.
The RFX Tteensy 3.X Dev board is exactly what I wanted to do. It makes all of the Teensy pins available for use and includes a 3.3V linear low dropout voltage regulator. The board is well designed and exactly matches all the pins of my Teensy 3.1.. Soldering the 14 pin SMD header is well explained however it does require some soldering skills and the need to very exact in cutting the female header strips to the exact size required and an ability to pay close attention to detail... I initially bought two and I intend to buy one more... Great Value for not so much money... An uncommon thing in these days. Thank You for a nice product.
Thanks Mats for your review! Fair criticism about the schematic -- I've now added a full schematic at the end of the "long" assembly instructions. Constructive feedback like this leads to better kits all around, so thanks for bringing that to my attention.
Also, as for the SOT package for the voltage regulator, as you've discovered you can straightforwardly mount a LD1117 in a SOT-223 package in place of the TO-220 package, if so desired. The SOT-223 pins line up neatly on the TO-220 pads.
While I deliberately chose to use all through-hole parts to make this kit maximally accessible to the less experienced with soldering, it's good to know there is flexibility in this regard when it comes to more experienced builders like yourself.
And Merry Christmas to you too! :-) I hope your nRF24 projects work out well.