There is a huge difference in wide vs narrow band 02 sensors. Wide band typically use the bosch developed UEGO sensor/cable setup, which allows for precise A/F measurements above the 1:5 ratio that a narrow band (stock setup) can provide. This is significant in that a modified car needs feedback greater than 1:5 ration for A/Fs if you truly want good control of those same A/Fs.
I can't say anything about the guage you posted but since it does not specify a UEGO sensor connection, my bet it it would use the standard stock narrow band sensor and thus, not provide a truly accurate or defined measurement.
Check this out for some detailed inforarmation:
If you do a google search for "A/F wideband" you'll see many examples of units to purchase. In fact, the link I put above has some very nice units for sale. Like you discovered though, these are not cheap. Just be sure they spec out as a UEGO type as many vendors out there say they are "wideband" when in fact, they aren't. To me, it needs the UEGO to be true.