The DigiDrive from Maxigrow is a decent quality digital ballast that features a 4-way dimmer switch to give you complete control over the power output to your plants.
The ballast will power 250W, 400W or 600W HPS or Metal Halide bulbs and includes a boost mode that increases output to 660W which is really beneficial during the flowering/fruiting phase. Be sure to pair the correct lamp to the output selected, so don’t be tempted to run a 400W lamp at 250W for example. This will save energy, but is a pretty pointless exercise as your plants will not receive the full PAR (usable light) range.
As with other digital ballasts, the DigiDrive will extend the life of your lamps by protecting the bulb from power surges and eliminating flicker. It also includes RF shielding so will not interfere with other electrical equipment in your home.
The DigiDrive 600w ballast comes with a 1 year guarantee.