Another difference to bear in mind is maintainability. If you plan to use the 570 for a few years or more, you will find that you own the housing long after it is deleted from Canon’s range. At this stage you may well find that getting replacement o-rings for the canon housing is difficult, whereas I think you will find that Ikelite will be able to supply replacement o-rings for a much longer time than Canon will.
Furthermore, if you find a need to service or replace control glands, you will find it next to impossible to get replacement parts for Canon housings, whereas Ikelite sell a service kit with all the spare parts you need. Because of the way Ikelite produce their housings, i.e. they use a consistent range of ‘boxes’ with controls placed accordingly for each different camera, and the fact that their controls are much the same across their entire range, you get better ongoing support for your housing.
If you plan to change to a different camera and thus different housing within a couple of years, then all of this is pretty much irrelevant however!