They are very different effects. MoL weapons only give the dark aura with stars. No crown store pack has that same effect. And with crown pack arms, you have to use that style to get the effect. MoL weapons have the starry aura even when you use an outfit style to change the weapon/shield’s look.
MoL weapons lack an environmental glow, though, so they will not light up areas or reflect off of armor like many crown store arms packs do.
ETA: Of course, for practical concerns, there is also the fact that you need to be using a MoL weapon to get that effect. With arms packs you can use any weapon.