Thank you for giving this a test run! Yes, no security warnings/updates needed will be a HUGE improvement!
Can you let us know what version of Windows or other OS you are using, and with what browser? That'll help us pinpoint any wonkiness you may be seeing.
With this uploader the images are uploaded through your browser (not our internal tool), that is why when you click the browse or upload files button a separate window will open with your files from your computer, and not within our upload window (like the current uploader does.) You should be able to minimize the window that opens if it's taking too much space and crowding your view.
You can only drag and drop images from your desktop into the upload area (don't click "browse" or "choose files" button if you plan to upload that way).
The browser may crash if you try to upload a crazy large batch of images at the same time, but that all depends on the size of the images, and your internet speed, etc. There should be no other reason for it freezing up though. Could you try it again (when you can afford to take a break from listing) and just try to upload a few images?
Thanks so much for your feedback!