Of the three partners the idea of expanding our working capital is mine. The other two are content to just let volume expand organically and if necessary raise our fees and offer a larger discount on direct sales to manage cashflow and prevent "outages". They have somewhat reluctantly agreed to at least attempt this alternative method of financing. The company is so far funded with cash.
As to why we don't get a small business loan? The reality is it won't happen. Not for a business with less than a year of history and certainly not at 5%. Getting small business loan is far harder than most people think. Honestly if you have good credit you are just better off getting a personal credit card and taking an advance (liability is non concern because any bank is going to require a guarantor on the small business loan anyways). Of course all that assumes you are a "normal" business. Mention bitcoin (or anything techy, confusing, or out of the box) and it is a non-starter.
I can finance this on my personal credit card at 9.9% APR however I am looking to refinance my house in the next six months and a $20K advance probably won't help my credit score. If I can't secure a loan the backup plan is to wait for the refinance to be completed and then draw an advance from my personal credit card. You also mentioned home equity. I would never finance a business venture with home equity. That is just poor risk management IMHO. Saving a couple % isn't worth the risk of losing your home if things go south.
As for the rate being punitive. I don't think the loan will be held for a year at least not at that rate. The note does allow either party to terminate the note with 30 days notice. If we can turn over the capital twice per month (we currently acheive higher than that) our margin gives us about 7% to 10% gross profit margin on the borrowed funds (which will cost us ~4%). That is a heavy price to pay but for short term financing it is manageable.