Other than size and quality of materials I don't see a difference between the RS Berlins and a Seaclone... They both have turbulent co-current with a lacking counter-current secondary feture. For the money there are much better designs out there IMO. The biggest issue I have with that design is it creates a lot of turbulance at the surface of the reaction chamber which limits "dryish" foam production (personally on designs smaller than 30" IMO a foam that is not dry but not wet is better).
Here's an interesting and informative link to keep in mind while looking for a skimmer. While it was writen for diffuser powered skimmers the basic info is applicable to all designs.
Skimmer Design 101
Chris