Wow, it hasn't even crossed my mind that someone would omit mechanical vario. That is the basis of glider instrumentation. Walking trough grid of last wgc most gliders had mechanical vario at prominent location in panel, I did not remember seeing one without.

I have two TE probes in my glider and have tried both mechanical and electric varios with same and separate probes. I did not find any differences plumbing them to same TE source.