If you put a Nerf football under the pedal, it allows you to feather the clutch easier.
It is also essential to make sure the clutch is adjusted properly. You basically turn in the adjustment bolt on the front of the motor until it just starts to drag (listen to the sound), then back off a little.
I got mine to where I could feather it stitch-by-stitch versus the 0% to 100% engagement it had when I got it.
Eventually though, I bought a SewQuiet 5000 motor and haven't regretted it. I highly recommend this unit.
If the unit you are looking at looks like this:
... I would avoid it. This unit is sold by several different vendors, but in use it buzzes and hums, and has very weak penetration when turned down to slow speeds.
Buy the SewQuiet 5000
if the Nerf football doesn't solve your control problem, you only pay once when you buy quality.