I find his legend being superior all around and paired with other damage + items makes it like a full heal and a killing blow. Move speed isn’t much needed for cal though as his double jump and charge attack gives him the best mobility.
The higher the remaining ammo in the mag when you reload, the more temporary regen you get (lasts until you reload again). If you reload with zero bullets, there’s no benefit. If you fire one shot and reload, you get the max benefit possible for the character. It’s not bad for regaining some HP when away from a pitched battle. I’m not sure I see 1,800 shards for it, though.