It is good electrodes for bias reference and references electrodes?
in Electrodes
Hello, guys, how you think this is good or not electrodes?

EEG Ear-clip Electrodes, Gold-plated Ear-clip Electrodes, Suitable for OpenBCI/TGAM/NeuroSky, Etc.
Comments
Just to clarify, Rand is referring a listing on AliExpress.
These can work. It's always wise to use the same electrode metals throughout the montage. Otherwise there is a risk of creating a 'galvanic' battery effect. Also, note that all 'gold' electrodes are typically tin with a gold plate layer. If the gold (over time) ever chips or erodes, again the galvanic effect can result.
William
William, thank you for yot reply. Yes, it is from Ali-express. How you think, Can I check the quality of electrodes if I measure resistance by Multimeter/Ommetr?
If you look closely at the photos in the listing, you can see that these apparently are plain gold cup electrodes, with a plastic spring clip, wrapping around. May be possible to replace the gold cups when / if they reach end-of-life. Or they may be glued in, can't tell. In any case at this pricing, I don't think you have to be that concerned.
Ohmmeter check is not going to tell you that much. If the gold cup connectors are properly attached, should work.
William, thank you!!