The TD1205 device is more than the usual Telecom Design Sigfox embedded circuit as TD1204 and TD1208, they are a all in one chip providing GPS antenna and RF antenna. Ready to use, to be clear you just need to plug a battery to use it.
In my point of view, for many applications not requiring more than 2 GPIOs, this product is really easy and chip way to design a SigFox product. As it costs around 55$ and you just have to add box & battery id sounds like the most affordable for small quantities. But …
This post is detailing what is specific to this chip ; read more following the link