This is correct (both answers)
There is no charge as far as the spread is concerned on a rolling bet, it technically closes at one price (mid price) at the end of the day, then opens at exactly the same price the next day.
There is a small financing charge (think of it as interest on the loan ie you are 10:1 geared) if you are long. Then there is a smaller fee paid into your account if you are short.
Long Trades:
How I calculate what to do is to determine how long you thing the trade will last. If it is only 2-3 days then I take the rolling bet. If you take the longer term 'contract', then you don't have interest to pay, but you do have a bigger spread.
Short Trades:
I alway use the rolling bet for shorts. That way I get the tighter spread AND a small interest paid into my account - you can't be bad to that 🙂