'Am using it and can confirm that the TTIG is a good choice for development. You can add a different antenna for better coverage as well (will void warranty!), if needed.
The GW is portable, easy to set-up (basically works out of the box with very little configuration) and quite cheap for what you get.
I have setup a single chan GW based on a RPi and Dragino as well. If I would have known about the TTIG before, I would have saved that hassle.
Setting-up your own GW based on single components is great for learning what exactly is going on. But if you are short on time and money and just need to create TTN coverage for your project the TTIG might be a better choice.