Sodastream--Godsend or Devil in Disguise?

Soooo I have a friend who had gastric bypass and has been drinking the Sodastream zero cal flavors and adding them to water (bypassing the carbonation process). So basically I guess it's just like drinking flat diet soda. Apparently it's made with stevia sweeteners, if I was told correctly? I drink a lot of mio and crystal lite and I know they are sweetened as well. So the question is, is this about the same thing as drinking mio and crystal lite with water or is it somehow the devil in disguise? I was looking at trying this in the future but I'm skeptical. What do you guys think?

I dunno I guess if you wanted like cola flavored water I don't see the harm it's sugar free and not carbonated.

 Depending on your program the caffeine could be a problem.  I used to live by my Soda Stream - Haven't used it since surgery, cant even give it away.

Ehhh, soda is such a controversial topic around these parts. But, I don't see anything wrong with it because I have drank a regular soda on a fairly regular basis since being about 8-9 months post-op without zero change to my sleeve capacity. It's a sugar free liquid, caffeine is not a diuretic so I wouldn't have an issue with it, nor would my surgeon.