I'd say illegal, at least in events played under WPA rules/guidelines.
Here's the description of a mechanical bridge from the WPA Equipment Specifications:
18. Mechanical Bridge
The mechanical bridge, also called rake, crutch or rest, is an accessory of the billiard sports table and consists of a stick with a bridge head mounted at its end to support the shaft of the cue stick replacing the hand bridge during shots difficult to reach. The stick or handle of the mechanical bridge is very similar in shape to the cue stick. The bridge
head has notches or grooves, usually at various heights, in which the cue shaft can rest. The contour of the bridge head should be smooth in order not to mar the cue shaft or rip the threads of the table-cloth when being used.
Since the EZ-Jumper has no stick or handle "similar in shape to the cue stick," it would not seem to conform.