Not that I was asked, but I have the actual Emco drill chuck that came with my DB, which is very good. However, I consider my Jacobs (USA) 7B on a 3/8-24 x MT1 arbor a very nice upgrade. However, it is a 0-.25" range, and sometimes I need more capacity. I have a larger Jacobs, but it is very long, so sometimes I will use my 2" Unimat 3-jaw chuck. (I normally have my 4-jaw on the headstock spindle.)
A genuine, original, M12x1 chuck will cost you a lot. The Jacobs on an arbor works well and costs less. I have been pleased with this setup - so far. The Jacobs 7B is just a bit smaller than the original drill chuck, and you get a little longer work space, even with the arbor.
Advice: Don't get a new Jacobs in any size; they are all made in China now and sold at Harbor Freight. You can find a good vintage, Connecticut-made Jacobs on eBay pretty easily, as well as the needed arbor. But you might have a hard time locating an NOS vintage set of replacement jaws and half-nuts, and an old chuck will probably need them unless it has been babied.
Whatever you do, best of luck.?
The Jacobs 7B is a very nice 0-.25" chuck with good concentricity.
Here is what the replacement jaw/half-nut kit looks like up close¡
Pachyderm