I am also coming from the Gear Icon X buds. These feel much better and the quality is really great!
I had my app open when I turned mine on, so no pop-up, but why this is a topic of discussion, no idea. They were super easy to pair and get using.
The Wearable App is also different than when I had my Icons. I like the way it has more options available from the screen wothoutndigging into menus or anything.
Comfy. Yes, even more so than the icons, which I loved. Without the onboard storage, when you put them in, they go right to phone mode, not independent, then a delay to phone.
Sound? They fit better in my ears, so they block out more sound which I like. The Ambient Sound mode is updated and much nicer to control. Sound quality is on par, if not a little better, then the Icon X's. Partially for the better fit, but also just a cleaner sound.
I have the new Buds as well and agree with all of your comments above. Pairing was super easy with the Note 9, much easier than the Icons.
A few other differences from the Icon X:
Swipe for Volume doesn't work (I knew this going in, but didn't think I used it much). You can alter the long-press touch control to adjust volume (left long-press Volume Down, right long-press Volume Up). However, if you do this, you lose the ability to use long-press to bring up voice control (Google/Bixby), which sucks.
I haven't had any issues with the buds charging in the case like I sometimes did with the Icons. They appear to fit better in the case.
The case, while much smaller and more pocketable, is also more slippery. So while the Icon would stay in my shorts pocket (yes, I'm in Texas so we wear shorts during the winter!), the Buds case has slipped out of my pockets a few times when sitting. So I have to check each time I get up or else never sit down.
Also the Icon X case has a release button which doesn't exist on the Buds case. Haven't found that to be an issue yet, but hoping it pop open at inopportune times.
I love the wireless charging - just plop it down on the charging pad!