I think the grunge is a different product more for seeding bacteria and such. The bugs are more about live stock.
Well my tank is already cycled so I guess I would need the critters more.....@NR53 what problems were you having?Different purposes. Grunge is mostly sand and sludge with the purpose of introducing bacteria biodiversity rather than critters. For me it did wonders in getting my tank balanced during the initial setup. Bottled bacteria wasn't cutting it and I was having all sorts of problems.