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.
The Outpost 2.0 bag is an improvement over its predecessor in that the mounting straps are removable however, the mounting holes in the bag do not line up with the top tube frame bolts on my Salsa Journeyman. The bag can still be used with straps however, it is frustrating to purchase a product specifically because of the ability to use it as a bolt on bag and then find you cannot use it for its intended purchase. Blackburn customer support was not helpful in resolving the issue.
-The BTD Team
Got this for my wife on her 46cm gravel bike and she didn't like using it - brushed up against her legs, wasn't large enough to comfortably fit her phone. I tried it on my bike and couldn't get it to sit securely around a steel top tube. Seems well made, but haven't really used it because the mounting system didn't feel secure to me. M