The MFDevice is a tool that has two modes of use: Wrench and ID-Tool.
The first mode, Wrench, allows you to recover any blocks in the mod by right-clicking on the block, the block should be inactive. It also allows you to right-click on any side of a directional projector to change the direction of the force field.
The second mode, ID-Tool, allows you to change a Blank MFFS Card into a MFFS ID Card by right click on any block, this is not to be confused with the MFFS frequency card.
The ID Card is not used in 1.9 (used in v2 or later of the forcefield mod) while MFFS frequency card can only be obtained by putting a Blank MFFS Card inside a Forcefield Core. If you obtain an MFFS ID Card and right-click the card on the ground it gives a message ":-) Wait for beta 6".
Note: ID Card cannot power projectors it is used in later version of the original mod (not in the current version of Tekkit) as a personal ID card that identifies you. This is a removed mod (source).