His principles are life changing if you follow them, and once you're hooked it's difficult to stop (in a good way in my opinion). 

Principle, interest, property taxes, property insurance, HOA fee, repair reserve?  

AKA it is a way to access some of the money you've put into your home while also making sure you can still afford your mortgage payments and other debts.You will need a renter in place as rental income is apart of the calculations when underwriting these loans in addition to the other factors you mentioned like monthly housing expenses (PITIA: principle, interest, taxes, insurance, assocaited fees ARV, debt outstanding.

Ultimately, your ROI criteria serve as a guiding principle, helping you make informed and strategic investment decisions tailored to your financial objectives and preferences.

The KISS principle is helpful here. 

This one strikes me as having some devious or less than ethical elements.

Loans are typically amortized meaning the percentage of interest paid compared to principle paydown is highest at the first month. 

An honest and ethical contractor will give you advice for free in hopes that they will build a relationship and get work.

@Joe Banks - Happy to provide whatever transparency into Eric's complaint that's within ethical standards and does not reveal any specifics of his personal situation.

When you put it in a spreadsheet and add in the interest to the principle every month it ends up being 30% annualized.