I looked at them a while ago.
The angle at which the cable enters the caliper and the way the cable is routed on the chainstay can result on a tight cable angle.
I guess it could work better if the routing was external.
Planet X description says flat mount but picture shows post mount.
https://www.planetx.co.uk/i/q/BRREVERFLT/reverroad-disc-mcx1-flat-mount-dual-movement--disc-caliper
Spyre knock offs?