I have been a Simple customer for a couple months now I absolutely LOVE the service. I have dug into what happens behind the scenes on their website and yes, they do pass more data back and forth than is always needed but they are using SSL so I'm not too worried.
You say you reached out to their security team and waited 8 days for a reply before following up, why didn't you just use Simple's support? I have reached out to them multiple times and always received a response within an hour. One of those times they redirected me to their engineering team so I could talk directly with one of their programmers, we exchanged 3-4 emails that same day. Should they have monitored this security email address you sent to better? Yes, but they provide the best support of any bank I have used in the past.
Pretty much I don't feel like the "concerns" you raised are all that important and in fact the whole post smells of FUD IMHO.
The reason I reached out specifically to their security team is because on their security policy page that's the email they provide to contact them regarding security issues. Reaching out to their security team wasn't some intentional move to try and not get a quick response, it was just what made sense to me at the time.
I agree that their support is usually extremely quick to get back to you and it's one of the things I love about the company. Except for these issues and their security team's response, I love their service as well. I'm not rooting for them to lose here, I'm rooting for them to fix the issues so we can all happily move on.
They have been much quicker to respond to people reaching out to them over Twitter today and I have updated the blog post to reflect that. I look forward to having these issues all wrapped up.