I'm going to do a small run of 9/16, 5/8 and 14mm speed handles to put on eBay in the next 2 weeks.
I'll post a pic of the design later, when I have access to a computer. Dealing with Photobucket on a smartphone is maddening.
I went with a relatively short distance between the knob and center socket, for a faster spin, and a shorter overall length as well. One doesn't need a huge about of leverage to tighten a vise.
I'm also pressing an 8mm x 8mm neodymium magnet into the back so it can be stored on any metal surface.
Here's a rendered image from CAD:
And 2 prototypes I fabricated and have been using in my own shop:
While visually, the design may not be quite as pleasing to the eye as others, I specifically designed it to be doable on a manual mill and lathe.
The center socket lets you spin the handle pretty quickly and get jaws snug, and the end socket gives plenty of leverage. The 5/8 handle is 5-3/4 overall length, and the 9/16 and 14mm handles are 5-1/4. Both have enough moment arm to damage the aluminum, and possibly even your vise. I kinda like the shorter length, as it helps discourage over-tightening the vise.