TDS figures are more reliable and appropriate than electrical conductivity for two reasons.1) Electrical conductivity measures the no. of ions, (charge carriers) both anions (negatively charged ions) and cations (+ ions), it cannot measure nonionised material in a solution, so you can have a solution with a very low EC value but very high TDS, this is especially a concern when we handle organic compounds. For eg if you dissolve 100 g sugar in 200 ml water the EC will give you no conductivity because sugar does not ionise, but the TDS will be high 2g/L enough, same is the case with urea. If you do not have organics and other non ionisable stuff then TDS correlates to electrical conductivity in an exact relation:

TDS (ppm) = 0.64 X EC (μS/cm) = 640 X EC (dS/m)

So actually it is the other way round, by knowing the TDS you can try evaluating the EC, but not the vice versa. Now 2) Eventhough it is the electrolytes that are acting as nutrients and the electrochemistry in the pot that is important, more important is the fundalmental of osmotic pressure. Plants are trying to accumulate ions etc against the natural gradient by using energy, now when you have high TDS the tables are turned, water will flow outside from inside the roots burning them in the process. Ever noticed that the green root tips on orchids turn black and brown on the slightest application of fertilizer? So you can easily kill an orchid with right EC water but the wrong TDS.