Since Lumin X1 supports SFP for optical network, we searched for a quality Ethernet switch that is also affordable. The current recommended configuration for Lumin X1 is to use a Cisco SG112-24 Compact switch, a pair of single mode 1310nm SFP modules, and LC-LC Duplex 9/125um Corning ClearCurve Single Mode fiber (from ebay).
The Cisco unmanaged switch SG112-24 is now sold at Amazon for less than USD99
The model Amazon ships from this link is the Compact version, not the wider rack mount version in the wrong photo shown in its web page above. The Compact version photo can be seen here at newegg: https://www.newegg.com/Product/Product.aspx?Item=9SIA36Z3US3666&Description=cisco sg112-24 compact&cm_re=cisco_sg112-24_compact--33-422-828--Product
Cisco classified it as End-of-Life, with last date of hardware support being December 31, 2020. So this is probably why the price is so low as compared to normal Cisco products.