As the schematics make clear the waveguide or microstrip network of the constrained feed makes that it far more expensive than the space feed. Prior to MEMs being available, lens phase shifters were ferrites or diode switched RF circuits. But new materials and the use of MEM phase shifters open up the option for lightweight systems. Two obvious potential applications for a lightweight lens are the aerostat and ship radars. Lots of volume and a desire for fire control quality narrow beams.
Weight is important for both.
The Radant Lens is a 1-D scanning lens that is an excellent application for MEMs RF switches. Scanning results from a linear phased gradient introduced in the E-plane at the output. The Conductive septums you see are separate multiple circuit layers that are periodically loaded by RF switches. Currently the switch is a PIN diode. Well suited to assembly automation and using low cost and light materials, this type of lens is suited to large antennas with scan in one dimension.