I've done quite a bit of testing. I have the Options>Image tab set to "Automatically resize images on upload."
1a. When uploading reasonably-sized images 1280 and 1936px wide, OR images already sized to final size, the resultant file sizes are huge, 300 to 500K. This is with "Scale images to max width 720px or max height 600px" checked. It actually makes the pre-sized originals 3 times the file size. At a ridiculously low setting of 20%, the image quality is no worse and the file size is still the same. Does this setting even work?
1b. When I uncheck "Scale images to max width 720px or max height 600px" the pre-sized images will upload without change, good result. This has to be used by a client, though, someone without Photoshop.
1c. When I re-size from the Manage Gallery page, the quality becomes less than desirable.
1d. The built-in WordPress upload with 3 image re-sizes is a very good result but not accessible from NextGen.
2a. What's even worse, the built-in Thickbox varies significantly in speed, even with some 60K images I pre-sized and uploaded. Load speeds range from 2 to 15 seconds. I've tried to make sure my computer isn't doing anything else while testing this. Is it most likely a script issue, a server issue, or a pipeline issue? A second pass through, with the images in cache is much quicker. But the delay is not much different on first pass with a 60K or 400K image.
2b. I have a slideshow on home page run by NextGen that takes 15 seconds for the first image to load after I upload new images.
3. Others need to use this, so I need a tool that's easy like this. I find it very convenient functionally. Thanks for any helpful feedback.