I use soda bottles and a carbonation cap, but that requires a CO2 tank.
Note: I buy sodastream syrups, but stay away from their hardware.
On the third hand, you can almost buy a CO2 bottle and regulator for the price of one of their gadgets.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk