I was having some issues with TPU clogging and ruining large prints on my v400, so I thought I'd try out the BTT SFS (BIGTREETECH Smart Filament Sensor)
https://www.amazon.com/dp/B0C7PZDBNC

I always hated the stock runout sensor as it felt cheap, didn't constrain the filament well enough for TPU at all and even with PLA when loading new filament it would get caught if the filament wasn't perfectly straight.

It didn't actually solve my main problem, it did kind-of sort-of detect when the clogs would happen, but it also seemed to increase the resistance of the filament path which made the problem worse. So I don't really recommend this upgrade for TPU specifically, but it works pretty well for non-flexibles. It's particularly good at catching binding filament which the stock sensor can't do. So if you have those issues, this is a drop in replacement that is strong, normal looking, lined up properly and very rigidly mounts the sensor.

It also has a thick flat spot on the bottom with holes in it for other potential add-ons that do actually solve the TPU issue. I'm still working on that, but this part seems pretty solid and is likely compatible with other sensors, though you may need some spacers or adapters in between. If there's a specific hole pattern or spacing anybody needs that should be pretty easy to add on here or remix.

Use supports and print it sideways the way it's oriented in the model picture, I used PLA but it would probably work fine using just about anything, it doesn't have to flex much for the clips to work properly and I've been using it for months at this point with no issues.

I removed the PTFE tube connector that is inside the v400 and just used the connector on the SFS sensor.