I have these on my touring bike for the last 3 years. koalabottle.com
Never have had one fall off the bike going over tracks or hitting a bad pothole. The steel ring to hold onto the magnet fits most standard water bottles, so you don't have to only use their bottle.

There are adapters available. Mounting slots on the cage would be nice, but it might let the cage slide down eventually.

Two adapters:
Mt Skidmore adapter

Problem Solvers adjustable. (This depends on one friction bolt, so I suppose it could slip if not tightened carefully.)

Thank you everyone for you input. I just ordered three King cages (stainless). Looking forward to their arrival.

Tried this on my straight blade carbon fork. No go. I can put the zip tie above the existing braze on for my brake cable holder and the bottle stays up where it should without falling but it just spins around too much and eventually rotates around closer to the wheel. I'm sure some duct tape would keep it there so I'll consider this idea as a distant third option :)

Unrelated to this but related to the original thread. All my bikes use the same cheap composite ones, Zefal "Spring", about $5. Over 10 years with no problems and I haven't broke one yet. They hold a wide range of bottles and they even stay secure on singletrack, over logs, washboard etc.. Only problem is small 16oz water bottles will sometimes fall out but I rarely use ones that small. Unless I wipe out, nothing else has fallen out. They do tend to scratch up the bottles but that doesn't bother me.

Not sure if it will work for carbon but my LBS has a tool to install braze ons (at least equivalents) so you can attach cages just like screwing them into down tubes and seat tubes. Check around.

^^ they're called rivnuts, and they install with a special pop-rivet-type tool.

First you have to drill the right size holes centered on the tube at the exact right spacing for a bottle cage.

Rivnuts hold pretty good but they can come loose and require replacement, and getting them out can damage the hole/frame. Welded/brazed bottle bosses are superior.

The specific construction of the Blackburn cage that I pictured at posts 6 and 14 allows for multiple ties down the center of the mounting bracket, not just one on each end, without interfering with the bottle. My fork blades are fairly large diameter at the top, also one zip tie loops around the top of a cantilever boss preventing slide down. Not sure if your carbon fork is beefy enough for a cage to be zip tied securely to it. Also looks like the center section of the Zefal "Spring" is raised out of contact with the tube so you can't use ties there. Those Blackburn cages are just $4-$5 and weigh 54g.

If zip ties are slipping, take an old tube and cut a piece to wrap around the fork before zip tying the cage on. The layer of rubber gives you a firmer grip and should help. The rubber will also protect the paint on the fork.

I'll try again with some metal cages I have laying around that do not have the bump in the middle like the Zefal does. Also try the inner-tube or similar wrap method. For my specific use case is for a short CCT I have coming up, I'll have a relatively light load and some spare room on the top of my rear rack for extra water but spreading some load to the front even if only 4lbs would be a nice option.

EDIT: I see the difference now.. The Zefal is flat on the back, works fine mounted up to a typical flat boss but inherently unstable and a tendency to roll when mounted directly to a curved surface (like my bossless fork). A Giant brand metal one I had laying around is concave and is way more stable.

I prefer the PDW Bird or Owl Cages, I have them on most of my bikes (except my vintage steed and my flat bar commuter thingy but that is just because I was out of them and had something laying about)

The main points are that they look really cool and fun, they hold onto bottle really well (including MSR fuel bottles) and why not?!

https://cdn.shopify.com/s/files/1/14...age_silver.jpg

Cages are cheap and easily replaceable so I just buy them from my LBS with their name printed on them. It's an easy way to give them some business and some advertising.