The issues that you listed are valid and there is not much you can do about it simply because of howe the browserLab engine has to work in order to provide you with the results you need.

We do all of our work on a publicly available dev server with the search engines blocked, meaning that it’s easy to update our clients on our progress and it doesn’t tie us to a single machine.

You need to understand how broswerlab works in order to see why it justifies being a hosted service: the screenshots that you get are actually taken by a load of virtual machines which when triggered open the page in their browsers (thus, the page is rendered natively on win/mac and in the specific broswer), take the screenshots and send jpegs back to the browser lab server, which then serves it in the window.

If they could build a desktop application, it would have to work as a web server for the time of the screenshot taking, which opens your computer up to a load of security issues, devours a load of resources and raises a load of proxy issues, where certain certain closed ports would block the access, thus making the whole thing completely useless.