Best rear light using a fixed bracket?

yep, a rear light with a bracket, kind of quick connection, no rubber strap mount…..

Cateye have always done excellent rear light mounts. I even use two rear light brackets to mount my rack on the recumbent! And every light fits the same bracket. You can even buy an adaptor for their Rapid strap-on lights (Rapids) to use with their square mount – have one of those too. Saddle, seat post and seat stay brackets are all available.

Garmin Varia RTL515 mount uses the standard Garmin quarter turn and is available as a dedicated seatpost mount (I have 4 to swap between bikes). Device comes with a strap-on bracket which is fine for my two aero seatpost race bikes, but the seatpost bracket is excellent.

no idea what model it is but I’ve got a Moon one that has a mount that’s clamped onto the seat rails. Works well and the light is great.

Only reservation would be if you wear a long coat or backpack that it might obscure the light somewhat as it’s right up under the seat.  this alos makes it a little fiddly to install/remove but I’m happy to live with that because it’s so tidy.

Hope Districts used to be a bayonet mount to a fixed clamp, not sure if that’s an option anymore though.

The Moon that I posted in the other thread has a really good saddle mount as mentioned above. I’ll get a pic in a bit

Most of the ‘better’ Moons come with saddle clamp, bungee clamp and fork leg/tube/bungee with bracket clamp.

Bought a moon nebula the other day. the mounts are ace as mentioned above