They are not bad, but they do need some modifications for marine tank usage. Since they use 5 micron sediment filters, the first step is to go to a local hardware store and buy a 1 micron sediment. Why settle for 5 when you can have 1. The second and third chamber should probably be replaced as well. They use granular activated and crushed coconut shell carbon. These are less than optimal as well. The purpose of the carbon is to reduce the organic material, metals, and most importantly chlorine from coming into contact with the RO membrane. Chlorine can destroy the RO membrane. The next thing you need to do is remove or add a tee to the 6th stage if your unit has one. This is the taste filter that adds TDS back to the water so it has some sort of taste. You should take the water directly from the 5th stage which is the DI resin.
I have compared the Aquasafe RO membrane to the Spectrapure membane line for line on their respective web pages and there is no difference in the two. Some things are filteres better by Aquasafe and some are better with the Spectrapure. It is a wash really.
Having said all that, by the time you replace the filters with the proper ones and add a pressure guage which is essential you might as well buy a unit that is already set up for aquarium use. There is a great product by Purely H20. It is called the Optima (see link at bottom)
The last thing you need to do is find out if your municipality uses chloromine in their treatment process. If they do then you will need to look at a unit that include a catalytic carbon so the chloromines can be removed.
http://www.reefperfection.com/index....ROD&ProdID=473