I have 20 colonies at an elevation of 1200 M  east of the rocky mountains near Calgary Alberta. I have them in EPS (Encapsulated Ploy Styrene) deep supers supplied by Beaver Plastic Products (http://bpgrower.com/langstroth-honeybee-brood-box/) .
The temperatures change widely and often quickly through out the day  here  (we call the warming winds Chinooks). I think the real value of the EPS box is it reduce the wide swings of temperature inside the hive by virtue of the better insulating values of the boxes. Bees seem to handle cold OK but they can get caught off guard and isolated from the main cluster. 
Other pros are - 
They are manufactured true to size - square.
The bottom and top edges of the boxes are true and seal well thus reducing draughts thus less propolizing of the bee boxes together. Easier to get apart.
They are light weight.
Cons 
Outside measurement are 3/4 "  - 19mm larger on each side. - standard tops - bottoms - crown boards - top feeders need to be re thought.  They do stand up well to mixing wood and EPS supers though.
They are more fragile to rough handling. I paint mine with high quality elastomeric paint  - it has been suggested that a coat of Weldbond sealer/glue and then paint will toughen them up considerably. 
Critter like wood peckers and skunks can damage them more easily. We just know that a big bad bear cares not what the box is made of.
The environmental issue of what to do with them at the end of life? Styro foam is always in trouble with this issue. 
In short I like em. 

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