I tried to use metal grease on the new tensioner, but it was jarring, probably due to the solid lubrication. Is it better not to use metal grease?

For the conditions you are asking about, we recommend either regular LS Bell Hammer Gold spray or LS Bell Hammer Gold Grease No. 2.
Metal grease is used for bearings that are subjected to loads in the several ton range (large bearings, stems, etc.), high temperatures, and water resistance. For daily use, the grease is also made for moving parts such as motorcycle stems and links that are subjected to high G forces.