And a bluer core than normal.

Although the thinner blades are a stylistic choice the series has used all along.

52 minutes ago, Lareg said:

I wonder why Kanan didn't use it when sparring with Sabine, since he was worried for her safety.

I doubt the Darksabre has this ability and he was likely worried she'd hurt herself with it. It's a reasonable concern that a block or parry could cause the blade to hit a limb or head, plus you tend to get quite fatigued when training with a weapon and you can inadvertently brush it against yourself.

The episode in question is the 2nd to last episode of season 2 of Rebels, entitled "The Mystery of Chopper Base".

1 hour ago, GroggyGolem said:

The episode in question is the 2nd to last episode of season 2 of Rebels, entitled "The Mystery of Chopper Base".

Thanks, Groggy. I thought it was near the end of the season, but couldn't check here at work. I just happened to luck into the clip I posted.