No objections, just think you will not end up with a better filtering system.
Thumbs up for looking into alternatives to those crummy pads, but loading that compartment with rings and sponges will make routine cleaning a big headache.
Let a stock HOB run for a year. Pull it off and do a real good cleaning. You will be shocked at the amount of gunk that has collected.
If I was you, I would certainly look at alternatives to the stock pads.
But I wouldn`t go stuffing gunk collectors in there.
$0.02
BTW: 6X9in. scotch brite pads will fit right in your filter. Last time I bought some they were around $7 for a box of 20. They worked great in my penguin 350s.