Personally, i use Lucas oil brand grease - when i use it in mandrel assemblies, i just give it a few shots and call it done- some is better then none at all.
A couple tractors i drilled and tapped the mandrels for zerk fittings - i dont over fill them, just a few shots every other mowing.
To cure a noisey MTD transaxle, i drilled and tapped one for zerks ( i cracked it open first) - helps alot in quieting it down - again a few shots every couple mowings .....
Im not a believer in using synthetic in every day mowers - the high dollar ones i suppose- but not run of the mill mowers. Cost just doesnt justify it. Regular oil changes should be done and itll last just as long or longer - i have a splash briggs motor old as i am still running , most are 20 plus years - all with regular plain oil- even the one brand new tractor i bot , still runs and still uses plain oil for 19 years.
I did however buy a couple quarts of royal purple for a mod tractor's motor- an 18.5HP opposed twin briggs - wanted to see about any power advantage on the stock 1996 governed motor - i didnt really notice any , but plan to use more when the tractor is rebuilt, just to add more protection under the extreme use , might add some royal purple gear oil to the trans as well.