Left foot braking is a case of retraining your brain. I've done it over 6 months to a point where I am confident I can vary the force used round corners.
The main issue is using left for braking at speed, if you can't "feel" the peddle with your left foot you can have a big accident.
I find using when left foot braking at speed round corners can settle the car while still still applying the accelator, again it's down to feel, conditions, speed and confidence.
However and this is the big one. Left foot braking is totally pointless with a manual transmission. Unless you've got a sequential gearbox that doesn't require you to use a clutch, you'll be back and forwards (left foot) from the brake to the clutch and (right foot) from the accelerator to the brake so you can control the car.
You'll be having a strictly come dancing session when driving.
...and I don't bother left foot braking when on track, for the above reasons.