If you ovulated on the 31st, you would only be 7 days past ovulation today. Most times, a bean hasn't even had the chance to implant yet until 7-10 days past ovulation so you wouldn't have any HCG in your system even if this is your cycle yet.
I would wait until 12 days past ovulation- which would be Sunday to test, but that's just me. I'm not a big fan of testing before AF is due.
FRERs are a little cheaper than digi's but it's up to you. Like you said, there's no mistaking a digi's answer.
Good luck!