The sea clone may be rated for 100 gallons but I can assure you it can not really handle a 100 gallon tank. There is no way, if you see a protein skimmer that can actually handle a 100 gallon tank next to a sea clone you will see what I mean. It did do decent with my 29 gallon, but I would not put it in anything much larger than that and to be honest it didn't do that good. When I gave the 29 gallon setup to my brother that is the first thing he replaced. I still had to do 5 gallon weekly water changes to keep water clean. There are much better skimmers that are hang in back that are a little more expensive. If you are planning a reef in the 55 I would recommend a different skimmer, as you will learn you need to replace the seaclone and it will be more expensive, an you will have a lot f trouble reselling the seaclone. If you are going fish only, and have small fish it might handle the 55.
The seaclone goes out of tune really easy, salt creep gets in the airline and disrupts the performance, the sponge filter will go bad really quick, the pump isn't the greatest and does not pull enough water for 100 gallons, and if you don't clean it every month it will get a gunk build up and not work at all. Also, everytime I put my hands in the tank the dang thing would flood and have to be retuned. If you properly maintain it, clean it regularly, run a cup of warm RO water through the airline once a week, it might perform ok. But even though the box says 100 gallons, this skimmer is really suitable for up to 30 gallons in my opinion. Also the collection cup is really small and you will be emptying it a lot. It is not a complete waste of money but most other options will probably be better, and you could probably save your money and just do routine water changes and get the same results as the seaclone because it really will not pull much out.
From my personal experience you do not want to go cheap on a skimmer, get a good one to start out with. It is one of your most important pieces of equipment and if you go cheap on it, you will end up spending more money down the long road.