Uno vs. Particle Photon

Has anyone ever used the Particle Photon microcontroller before? The project I am working on requires us to retrieve data about the weather and control an object through "if" statements about the weather condition. The Particle Photon is already configured with the app and has partnered with Weather Update and IFTTT, so it fits what we are doing. However, is it compatible with shields, such as a motor shield? I haven't worked with this particular microcontroller before, so I was wondering if anyone else has and can provide some feedback about its pros/cons as opposed to the Arduino Uno for such a project?

is it compatible with shields

No. Not the same physical format, and not 5V capable (5V "tolerant", though.)
The last time I looked at a Photon (which was quite a long time ago), it seemed to be one of those devices designed to be used with the companies could-based services for actual network communications, which ... prevented me from being interested (ie, I perceived that it wouldn't talk directly to local networking things. An interesting and perhaps even useful model for IoT security, but something I personally disliked...) That may or may not be still the case.