The HOBs are really more of a chemical filter than a biological one. There may be some biological activity in the cartridges but that is not their main purpose as these things need to be cleaned to maintain filtering abilities.
For a Biological filter, I would use one of the larger sponge filters in conjunction with your HOB. Sponge filters are designed for Biological Filtration. Considering you have an Oscar ( a really dirty fish when older), you want the best mechanical filtering you can get. Frequent cleaning of your filter along with routine water changes will keep the tank clean and the fish healthy. This will reduce the stress on your biological filter in the long run.
Hope this helps