Assuming the patient does not have any skull fractures... the eject system is just another method of removing a helmet. I do have an issue with a provider installing such a device under a helmet that was not previously fitted with one. You have little control or knowledge about the condition of the liner as you install the device. I'm sure it works fine, but the instructions do caution you not to use the device if there is structural damage to the crown of the helmet.
For Football players, if you must do CPR on them, you can leave the helmet and pads in place. Cut the sternal laces and begin compressions. Remove the facemask as detailed earlier in this thread. Once the face mask is removed, you have airway access, OTI by use of normal c-spine precaution techniques is possible. When you have time or an extra set of hands: cut the straps above the chest piece that attaches the shoulder pads in place. Cut or remove the straps along the side of the ribs. Lift the chest piece off. You now have excellent access to the chest while maintaining in-line stabilization.
If you do have to remove the helmet, removal can be eased by popping the padding below the ears out of the helmet.
It is in situations like this where knowing how the helmet and pads are constructed and fitted that can make a difference in determining whether or not you should remove the equipment at scene or later. Most, if not all, equipment that I'm familiar with is radiotransparent. You can shoot x-rays through it and get decent plain-films. If it'll fit in a CT scanner, you should also be able to get decent enough CT scans to determine if there's a fracture or vertebral body displacement...
By the way, helmet and pad removal can take longer than simply cutting off stuff.
Note: when doing Football standby's, you might also consider using longer straps than normal to accommodate the extra bulk of the pads.