Despite the advocates of spend big = quality, bleating on about future dangers etc, I advocate doing the best research analyses you can ie cost : benefit.
With an experimental aircraft, you have great freedom and with it responsibility, to do the right thing (whatever that means for a given project).
E.G. You can easily make a flexible transponder antenna for the cost of connector, some multi strand copper wire, solder and shrink tube, at a guess $5 all up.
IF your Chinese coax will do the job, to an airworth (transmit & receive) standard - go for it. Spending x 10 will not make the system more efficient or have any implications on safety.π