In Australia the oil is $12 per bottle, the filter $16, the gasket $8, and the washer $4 so the 'kit' is cost effective for me.
I do alot of oil changes as I give my baby a severely hard time at the track.
When I swap to Castrol 4T semi synthetic 10-40w and order the filters & gaskets online in bulk, then I'll change, but for now the kits are great.
I prefer to run the std oil till the bike has done at least 10,000 hard km.
Bottle being a litre?