Hi Itzoe,
The #4 is the best bang for the buck considering the price, size and build quality of these units. It is comparable to the Cookshack commercial units, but a much better deal. Steve even give you a 3 years warrantee, CS does not. The replacement parts are much cheaper to buy, easy to replace, although I haven't had to yet (I purchased my #3 about a year ago).
The CS are also great units and have built a reputation for themselves, but you are paying for the name, parts are much more expensive and at the end of the day, the SI will give you the same results as the CS. Steve stands by his products, parts will not be an issue and your return on this unit will pay itself off in no time compared to the CS. Personally, I wouldn't hesitate to purchase a #4 with money saved in the bank.