I have seen the product tested. Here's my take:
1) Will you save money? It depends on how picky you are. It comes out about the same as the store brands, or the major brands on sale. It costs about the same as the cheapest soda, and you'll never make up your capital expenses. Also, if you don't have a dishwasher, the bottles will be a REAL pain to wash.
2) Is the product good? Every syrup I have tried (regular and sugar free) have been excellent. I have even bought some syrup to add to my own seltzer. And the ingredients are good, too; all the sugared sodas are made with cane sugar, not HFCS or even regular corn syrup. And the carbonation unit allows you to control the level of carbonation.
In short, you get a better product at a pretty reasonable price, if you're willing to eat the $99 buy-in and don't mind the cleaning required. If you already have a seltzer maker, consider buying the syrup.