There seems to be a common misconception that because the MR helmet was scanned from an original helmet, it is perfect and virtually identical to the original. Unfortunately we are not quite in the Star Trek age yet and while scanning technology is amazing, it is far from perfect. Likewise, while the MR helmet is extremely nice and I would encourage anyone to get one, it is NOT perfect and is NOT exactly like the original.
While every original Fett helmet is slightly different, they share many common features and are more or less the same. Some time ago, I had the privilege of comparing the MR helmet (scanned from the pp3) to a FIRST gen casting from the Preproduction 2 helmet. Below are comparisons of the two helmets, showing the similarities and differences. I think most of the comparisons are pretty good except the back shot in which the PP2 casting helmet was tilted too far back, making the brow band look odd.
The MR is a commercial helmet, readily available to the public while the PP2 casting helmet is not. This will probably make the MR seem better in the eyes of some, and I think from a costumer's standpoint, it IS the better helmet, but in terms of sheer accuracy, I think these pics clearly show that it is not perfectly accurate to an original. The PP2 casting helmet is a direct cast of an original helmet, and has all the original blemishes, warps, warbles and ugly spots that a real screen used prop has. You can see the dome is lumpy and uneven. The brow is warped. The aspects are very rough and asymmetrical. The MR on the other hand is based on an original, but to a degree, has been idealized. It is a gorgeous helmet with smooth surfaces and very clean, flowing lines. To me, it represents what the helmet should look like and does look like in our heads. Ones preference comes down to whether you like absolute accuracy, or idealized perfection. Neither is wrong, but I feel it IS wrong to use the term "screen accurate" interchangeably with terms that really mean you simply like the way a helmet looks.
Thanks to those who made these helmets available for me to compare and photograph. You know who you are.