I know of several ppl who have used this brand and they love it... I wouldn't take it to any dpeth though but you wont have to worry about that in a shark cage...
Give it a good test at home by just filling it with air and placing it underwater to check for leaks... get really familiar with the sealing mechanism to ensure it is sealed properly before you take it underwater. With a soft plastic case like this check out the shark cage good before hand and look for places where it may get snagged up and potentially rip the housing... depending on the cage sometimes the bolts used to assemble it can catch objects and in this case rip the plastic. You're gonna be temped to stick the camera through the opening for a clean shot.. dont do it with a soft plastic housing... or any housing for that matter

A friend of mine lost a great camera that way... took a few minutes for the shark ot realise it wasnt shark food.
If you buy this unit... when you are getting ready to enter the cage... ductape the seal as an added precaution from being opened by accident.
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Canon 7D + 50D + EF 100-400mm f/4.5-5.6L IS USM + EF 24-105mm f/4L IS USM + EF 100mm f/2.8L Macro IS USM
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