The handle works well in my hand but without much room to spare. My hands are fairly large but they are longer than they are thick.
You're right about the sheath. Mine has a retention screw that could be tightened. Unfortunately, the retention point puts a small amount of plastic (not kydex) against the metal guard. That plastic wears away, leading to a need for increased tightening, until there eventually isn't enough left. With the retention points ground away, the sheath still holds (and better than some loose leather sheaths I've had over the years) but it's annoying. I'm actually planning to send mine out for Kydex because I love the knife.
The quick-adjust belt attachment is worth talking about. For those who don't know, it uses a locking tab to fix the orientation. You can press the tab, rotate the sheath it on your belt, and then lock it into eight or so slots for different cants. (I mostly change from vertical to horizontal depending on if I'm driving or doing other things.) I have a few other fixed blades that use the same attachment and I've really fallen in love with it. (The other knives use better sheaths in better material.) Whenever I get around to upgrading my Jager sheath, I'll be sure to have it set up to reuse the belt attachment.