Caveat - I sell both...here's some opinions for what they're worth...I'm trying to give a balanced view...
The RDX is a good quality, entry level plastic housing, and it's controls are pretty good, better than Ike, at about the same price level. It's somewhat heavy, surprisingly. Controls aren't all that ergomomic, but decent, you'd get used to them. It does not come with handles and a tray, and they will add $150-300 to it alone.
It can use S&S NX Ports, but you have to adapt them with an RDX port base. There is only one RDX Standard Port. There are gears for a decent selection of lenses, but not as many as you'd like. You can use the Port Base L + the Zen dome ST with it.
IMHO, the S&S Port Charts are a bit bewildering, as they have changed parts, especially on the macro side and you will need up to 3 parts for one lens, plus a gear. I've seen no less than 3 different p/n for the same or nearly the same ports now. Hopefully this will improve.
I think the RDX housing is a good place to start - if you're not planning on expanding it - or you are planning on moving up to an MDX DSLR housing in the future.
Nauticam: I shot the NA-600D prototype in Sept. I'm a Nikon guy, so I was gritting my teeth a bit, but got some good images. I have to say I really do like the Canon sensor.
The housing was great, very well layed-out, good controls, ergonomic, balance and weight quite good. Nice and small for a DSLR. Big difference is that it's highly-machined aluminum. It includes the handles, btw. Has locking ports, a leak detector (the RDX doesn't) and a great selction of ports and gears, easy to use and understand. For instance you can buy the 60mm macro port and then just use a 30mm ext for the 100mm macro. Both are threaded for a diopter. I just spec'd one for the 150mm Sigma macro, several options, but easy to figure out. I wouldn't even attempt it with S&S.
The Nauticam is much cheaper and easier to expand on. And you won't be throwing away port bases if you change bodies later.
As to the costs - This is where it gets interesting.
I've just done some comparison quotes of both systems with setting up a Tok 10-17 in a Zen 4" dome, a 60mm and a 100mm. Because of the tray/handles and all the adapters that the RDX/S&S requires to use their new threaded macro ports (and I wouldn't go without - you need the working distance) - the costs of both systems becomes very close - within around $400 or so. And really, you have a much nicer aluminum housing with the Nauticam and less parts to pack.
Hope that helps,
Jack
