I've been using this bag for about five months and it's still on my road bike...a sign that it works well for me. If it didn't, it would have been consigned to my pile of seat bags and similar accessories that looked like a good idea but for one reason or another didn't pass muster for me.
My phone fits fine. But it's a smaller phone than most...originally an iPhone 5S and now a 12 mini. So let that be an indication.
The movable partition allows me to set aside a separate space for my dirty cleat covers. Very handy.
By using this top tube bag my smallish seat bag just stays under the seat untouched from ride to ride holding the essentials like a multitool, CO2, etc. I stash my ride-to-ride, grab-and-go consumables like phone, cleat covers, wallet etc in this handy, reasonably compact, and easily accessible bag before heading out.
When on my smart trainer, this bag is where I put my phone for quick access to change my audio source...and a washcloth for blowing my nose. Super convenient.
It's very stable on my bike, which doesn't have top tube bosses. It comes with two rubber grommets to place face down in the bag's holes where the mounting screws would go. When the straps are cinched tightly around the top tube the grommets help keep the bag from shifting. Note though that my bike is titanium, and the top tube may have a larger diameter than others, and that might help keep the bag stable.
I've had no interference with my knees but when I dismount and straddle the bike I touch the rear of the bag. Not a problem...just a minor annoyance. Note: my effective top tube is 56.5.
So yeah, this bag works well for me.
Thank you for your feedback.