FWIW I use Stens filters and have been doing so for a long time with absolutely no problems.
Stens claim theare OEM and visually they look identical.
IF you have or bought additional warrantee then pay the extra for genuine Kawakasi filters & oil till warrantee expires and keep our receipts.
It makes it hard for them to weasel out if you have been doing the right thing by them and when it is all said and done what is $ 20 extra for consummables on an expensive mower once a season.
As for the hydros check carefully the service schedule they generally go a very long time before service is needed and you can be doing more harm than good .
Again for Hydros, go with the makers branded filters as hydros are very sensative to things like oil filter back pressure and some seem to rely on the bypass valves to give extra over pressure protection.
Down here OPTI ( Stens brand ) oil are doing a "Double your engine warranee" promotion so that might be worth looking at if it is running in the USA .