Standard packaging of RUTX50 comes with 4 mobile antennas included, specifically matched to operate with the router over a wide range of frequencies.
In comparison to the antenna you have referenced, packaged antennas are more suited for operation with the router.
As you have presumed, PR1AS420 is not designed for operation with 5G, specifically, bands above 2.2GHz. It also has lower maximum achievable gain.
Overall, PR1AS420 is not a suggested option. In addition, for optimal performance, it is highly recommended to use RUTX50 with all four antennas attached, as antenna connectors for RUTX50 serve different purposes than connectors on RUTX14.