Very good replacement for canned Mountain Dew. I've been drinking Mountain Dew for a long time, usually canned. I decided to try these Sodastream versions and I was pleasantly surprised how much it matched the original. It's not a perfect replication, but it's good enough for me. I'm no longer buying canned soda because of this.
I like to add a little grenadine to get a touch of cherry. Still solid without it though.
The main thing is getting your carbonation right and your syrup level.