They have filmed new miniature effects.

The disks have new scans of the original episodes as well as versions with new updated vfx.

Haven't seen it since it was on TV when I was a kid in the early 80s. I'm assuming it must have been a rerun as I'd have been to young to remember it for most of the original run. However it still has always stuck in my mind as one of the best sci-fi series and one of the few where the "good" guys lose. I'm amazed it's never been rebooted or turned into a film.