First, my retirement funds are things I'm _very_ protective over. Aside from a blurb saying "We use a third party service with bank-level encryption to connect your accounts," I don't have any reason to trust this site. What's the 3rd party? Can you link to them? Why should I trust you _and_ them? The idea of giving your site access to my bank accounts is... scary to say the least. You need something on the landing page to walk-through how this wouldn't allow someone at your company to somehow empty my accounts. ;-)
Second, the site seems to imply knowledge of actions possible that aren't obvious. For example, my employer sets up a 401K through an investment firm (like Fidelity). I have no choice in that. Likewise, Fidelity charges a set rate, of which there's nothing I can do. My choice is to either participate or not. Unless the site is potentially looking into extra charges (by fund?) that I can switch, or multiple 401K accounts from past jobs that I can roll-over or do something else with, I'm not sure what this service offers besides telling me what I already know?
Assuming there is plenty of choices I do have control over (re: second comment), it would be nice to enumerate what some of those would be on the landing page or even put together a little animated video describing the problem, what options an employee may not know they have available to them, how the site (read-only, and hopefully not saving anything) collects information about the accounts, and can present me with information and options that "with a click of a button" can save me money.
Great idea! Hope these comments help.