So take what I'm going to say as only a semi-educated opinion, based on a little online reading a while back.
My sister asked me beforehand whether I wanted one of these for my birthday. While the initial thought sounded kind of appealing, since I'm really into cooking from scratch, with a lot of kitchen gadgets, after reading some online reviews and sites, I said "not for me, no thanks."
The reasons I decided it wasn't that great of an idea:
The syrups the company sells all contain Splenda, even the non-diet flavors. Mind you, I don't mind Splenda, and I drink a lot of diet pop (we call it pop here in Michigan, no one says soda), mainly Mt. Dew and some Pepsi Max, but when I want to splurge on the calories and have a Coke or Pepsi, or I really need that 3:00 PM sugar rush to get through the rest of the work day, I want something with sugar. Plus, while the company makes versions of all of the most popular flavors, I don't want to trust some generic version of the specific flavor of Coke, Pepsi, Mt. Dew, etc. -- alternate brands, such as store brands of colas, root beers, orange, etc. can be pretty bad compared to the specific taste of named brands, IMHO -- I especially hate a lot of off brand and store brand colas, which to me have a funky, musty taste, nothing like Coke or Pepsi or even RC, which is decent.
The quality of the water source is important, and our tap water here is disgusting as is from the tap. I buy bottled water to drink, and put tap through a Brita to make ice. So, that would be more water to buy or filter for me. Something to consider -- as some of the reviews say, if you don't start with good tasting water, your pop won't taste good, either.
What it does -- all this product really does is make seltzer water/club soda -- you then just stir in the syrup to flavor the pop afterwards. Well, I've been doing this for years by mixing club soda with juice or syrups, and I can buy a 2 liter of store brand club soda for $.88.
You need to periodically refill the gas cylinder - it's not purchased, it licensed from the company, so only they can do it for you. And, you need to send it in. So, to have an uninterrupted supply, you need to purchase a second one while yours is in transit. Many people also suggest buying multiple bottles, since the carbonation bottle is specific to the unit, nothing else fits it.
So, my final analysis -- not worth the expense or hassle -- I can buy a lot of club soda for the cost of the base unit plus the ongoing expenses of carbon dioxide refills and bottled water, and I wasn't sure I would like the finished product when compared to the name brand pop flavors I drink.
Your mileage, as they say, may vary.
I relied a lot on this site to make my decision, I thought it was fair and balanced (unlike Fox News!), giving both the pros and cons of the product line:
http://www.mysodastreamreview.com/
= new reply since forum marked as read