Hey Ash89GQ,
The Foam Cell Pro is a much larger shock absorber, and is constructed of stronger and thicker materials. The Foam Cell Pro uses foam cell technology over standard hydraulic design. Both are re-buildable and valved to suit heavy duty springs (though each has their own specific valving). The Ironman 4x4 foam cell pro is available to suit a range of lifts (2", 4", 6" & 8"). Beyond that mate it comes down to personal preference and price (Ironman 4x4 Foam Cell Pros are $220 per shock - to suit a 2" lift).
In terms of stronger and thicker, our shocks have a 3mm wall (as thick as our bullbars - which makes them bloody tough) where as a standard aftermarket shock (and this isn't specifically a Koni) are generally around 1.4-1.6mm thick.
I'm not going to slag the Konis. They are a good shock, but I believe the price and strength of our foam cell pros (as well as their excellent ride) makes them a very competitive shock in the market.
Hope that helps mate!
Cheers,
Matt
Ironman 4x4