My "housewarming" gift when I moved into my current apartment a few years back was a Soda stream soda/seltzer maker. I've used it pretty much several times a week and at sometimes even several times a day! My counter space is at a premium, but this is one appliance that has earned the right not to get put away in the cabinet.
Life in NYC means A LOT of shlepping groceries. It's not fun to have to carry a couple of two liter bottles along with all the other weekly or pre-Shabbat purchases. Even with a cart, it's still a pain. Then there's having to separate the plastic bottles to recycle. When I've had a few guests over for shabbat, that could be several bottles of beverage used with the bottles just lying around until I can take them to the apartment basement post shabbat.
Sodastream has solved that issue since the concentrates are much smaller and lighter to carry. Or just use plain water and make seltzer for just the cost of the CO2 used. The syrups are OU certified. Many rabbis do permit using Sodastream on Shabbat since there's no electricity and it's just mixing CO2 into liquid. I also like that this is a Israeli based company and manufacturing is in Israel!
I know the company likes to tout a cost savings of using their CO2 supplies and syrups versus buying soda by the bottle. Perhaps there is, but really I like not having to deal with big bottles. Besides regular soda, I like making Italian sodas and sparkling water mixes with a bit of juice. Cranberry and Apple juice are a bit too concentrated and high in calories on their own, but mixing it will a bit of fizzy seltzer is a nice way of having a flavored bubbly beverage that's not high calorie. Another option for me is that I use flavored syrups, preferably sugar-free ones like they have at Starbucks. I like Cherry, Almond, Vanilla, Hazelnut Italian sodas. Basically it's just making the seltzer and adding the syrup. Even more adventurous is taking the flavored soda, and turning it into a delicious egg cream. See, I told you I am a huge fan!
SodastSodastreamream has expanded greatly since I bought their product online. The concentrates are now being sold at many retailers including Bed, Bath and Beyond and Best Buy. However, I still use the site for ordering the CO2 replacement cartridges. Still feel a bit funny taking an empty canister to get swapped out. Plus my neighborhood has free delivery. I also use the code FREEMIX to get a free concentrate when I order a CO2 refill so it makes it worthwhile to order online.