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The Masiv's all brass soldered construction is quite stout and sturdy. Masiv doesn't make any claims about improved burst strength over stock but we bet it is a lot better than the stock 3 piece radiator with its crimped on plastic end tanks.
The Masiv radiator has this cool coolant filter. This is a really nice touch. The Masiv core has three rows of tube and fins. This would be traditionally called a triple core radiator and is the traditional way to build a heavy duty racing radiator. We questioned the use of brass in a racing radiator since the thermal conductivity of brass is less than aluminum. Masiv told us that since brass is stronger than aluminum, the tubes can be thinner and this would make up for the difference in thermal conductivity of the material. Would this work?
How does Masiv compare to CSF? Well the CSF is TIG welded aluminum with a tube and fin heat exchanger design. Masiv has a traditional design with 3 rows of small tubes. The Masiv is constructed of soldered brass, the traditional old school way of building a heavy duty radiator. 
Although the CSF is a lot thicker than the stock radiator, the Masiv is a lot more massive still being about 40% thicker than the CSF. Both radiators are deigned to drop right into the FR-S/BRZ twins with no mods to the car. Note that the Masiv has larger, higher capacity end tanks as well.
The Masiv is a lot heavier than the CSF radiator weighing in at 16 lbs.
The CSF radiator weighs in at a feathery 6 lbs. The Masiv is more than twice the weight of the CSF!
