I have an Invasion and a Plasma Cell..  The specs say its the same as the cell.. but I have read that the cover may be a little stronger than that on the original cell.  I have a little different layouts on the two balls (cell with pin under ring, MB strong and Invasion with the pin above ring with MB strong), but pretty close. 

 

Overall, I feel the two balls are quite close in total hook.  The looks I get a quite a bit different.  The cell seems to start up earlier and have a much quicker transition/change of direction.  The Invasion seems to get a little more length and has a much slower transition or smoother breakpoint (the length differences may be due to the pin positions though). 

 

I get the feeling that the Invasion is a little more predictable and its not going to "jump" on me as much. 

 

I think the difference in the change of direction makes them sufficiently far enough apart to warrant having both (at least that's what I tell myself). 

 

S^2