Gridllr.com is updated today with a small improvement. The Download button on image posts will now download the image immediately (one-click downloading).
It will always download the largest size available from Tumblr, usually that’s _1280.jpg.
Note that often the poster’s original image is less than 1280px, so the file you download might be less than 1280px wide. There’s nothing we can do about that. But you can try the built-in search function, which uses TinEye - TinEye can maybe find a higher resolution version of the same image somewhere else on the web. Sometimes it does, sometimes it doesn’t, there’s a bit of luck involved!
If there’s any feature in Gridllr you’d like to see, you can mention it in comments.