Good afternoon.
Initially your project aroused interest. But then this interest was lost because of double conversion and inadequate interest. And if you do not make changes in your system, your project will be of little use to anyone.
Why does NH count the balance in bitcoins? Yes, because it avoids the exchange from $ to bitcoin (like you, with a loss of 3-4%)
You balance the same in $ - and you need to print in $ or USDT.
Not see double-conversion, just displaying the balance in dollars at the current rate. I don't think it makes sense to drive the currency back and forth.