I have both, it's easy when they're side by side!
The clone sleeve is thicker than the authentic. If you put that sleeve over the authentic tube (and it fits) you will feel the difference in diameter, i.e. your finger will feel an edge when running up and down over the mod. The pieces have incompatible threads as well so they're not interchangeable with each other.
The firing pin on the clone is solid whereas the authentic has a groove milled in its center.
The magnets aren't as powerful on the clone so the switch is much easy to press and fire. The lock, however works well.
I guess the differences depend on the quality of the clone. But at about 15% overall the cost for a full kit, it isn't bad.
And like the authentic, it hits like a mofo!