Is this TDS meter good?

[Buckeye Hydro]

If you check with the manufacturer they actually hide the fact the 3 meter dosent work with RODI units for saltwater.

I don't think anyone is hiding anything here. TDS meters used in this hobby are not for the measurement of saltwater. The TDS of seawater is typically > 35,000 ppm - and that is beyond the upper range of the meters.