In episode 9.2,
Clara and Missy escape the Daleks by using the energy from the rays they shot at them to power their teleporters. Missy explained how the Doctor had done something similar in the past, but the difference is that in Clara and Missy's case the rays did not strike the device directly, which implies it's enough to have a device that can use the energy anywhere on yourself.
In theory it may even be possible to use a device that does something other than teleport you, or maybe nothing at all.
Using the knowledge above, what stops anyone who has access to such technology to use it as a shield, allowing them to get shot by Daleks with no ill effects?