If you want to try submithub out, be ready to pay with a card, regardless of what the UX seems to imply. It seemed like a good service, but now I don't see myself dealing with them.
When going through the submission process you'll see it prompts you whether you want to use your standard (free) credits or premium credits. If you don't have any premium ones -- and don't want to buy them -- make sure you stick to the 'standard' path.
The core idea behind SubmitHub's "model" is that for decades it's been near-impossible to catch the attention of bloggers/playlisters/curators/whatever. Our system dangles a carrot (~$1) in front of them to guarantee a response+feedback about your song (with the ideal outcome of course being that they share your song - no additional costs involved).
For pro musicians who are committed to your product as a promotion path, perhaps they don't care about that credits ambiguity because they go in with a marketing budget and know what they're going in for. For me, I will stick with making music for fun. I wish your team success at their mission.
There is an interview with the founder on a podcast somewhere that's quite informative. I'll link to it if I can find it.
I had never heard of Soundcampaign though. Will have to check it out.