that's great, however

In particular, this happens for RF frequencies that couple the Rydberg level resonantly to other nearby Rydberg levels. For sufficiently large fields, the atoms are receptive to a broad range of RF signals via the AC Stark shift.

meaning there's physical limit on where these bands need to be, outside of these regions it's less sensitive, and it's mostly microwaves anyway (authors tested 16-20GHz)

we are able to make very compact extremely broadband receive (and also transmit) antennas for microwave bands, it's a log spiral antenna backed with cavity. easily can reach to over 40GHz, much simpler, smaller (counting all optics) and probably with much better sensitivity. already used in radar warning receivers, and has nice property that on lower end it's limited by size, but on upper end on precision of the central section - so can be made really wideband

also that's really just a transducer, still needs a box with lasers and some other machinery that allows for demodulating that optical signal. "RF detector that doesn't contain metal" is a weird advantage because there's usually a large amount of metal connections required to actually do something useful with that freshly collected signal

actual article https://pubs.aip.org/aip/apl/article/123/14/144003/2914151/Distant-RF-field-sensing-with-a-passive-Rydberg