I'd totally agree with everything that's been said so far and I don't know of a better place than this where you'll get well thought out professional level answers to almost any machining related question asked. However for a lot of home shop guys, those same answers while being technically correct and unarguable, they are from that professional level perspective. Speed of use, accuracy, repeatability and any tools long term durability at the commercial level are primary and the costs to get that would be secondary. So everything already said is completely logical.
I've been exactly where you are now and for most of us with a home shop that speed of use is probably a bit less important. So yeah one of the cheaper 4" or so clones of the Kurt mill vises for a home shop DP such as Dave M linked to could be much better than anything else on your list. I've also been there and done that mistake so now wouldn't buy anything like what it's price would actually get me for my mill. There in my experience Kurt shaped objects only, and the resemblance to one stops at the exterior. With the addition of a cheap set of parallels, there probably quite good enough on an off shore DP. But can your DP even match what one of those vises has for there lower end accuracy? You haven't said, but it's probably a pretty safe guess your wanting a better vise for one of the usual off shore bench or floor standing consumer grade drill presses? If so and unless your into watch making sized parts there simply ISN'T one of those made anywhere in the sub 1,000-1500 lb range that isn't so flexible to make a fairly expensive, heavy and accurate vise your paying to get almost pointless because of the overall design the DP itself has.
If you want truly square and perpendicular holes and you obviously do or you wouldn't need a DP, then the table has to be correctly trammed to the spindle. While your doing that, try applying maybe 20 lbs of extra hand pressure to the front edge of it's work table while the indicator tip is in the same area. It's for that reason I got rid of my 150 lb floor model DP the day I got my BP clone even though it's spindle and keyed chuck had an amazing low level of run out for what it was. Any tool is a combination of design and manufacturing compromises. And every single one of those home/light wood working DP's fail because of that built in problem. Watch any Youtube video with these light weight DP's being used and you can easily see that table deflection happening. Changes in work piece and fixture weight, drill size and feed pressure literally bends that table a constantly variable amount no matter how accurately it's trammed. For sure a better vise will help, and it's certainly worth adding one. But the tool it's being used on will still have that massive defect that can't be easily solved no matter how good the rest of the machine, it's alignment, run out and work holding is. A fast acting accurate $350+ DP vise makes perfect sense on a heavy industrial level DP that's built to use what it can offer. If you already have that, then sure I'd most certainly go in that direction. I'd even do so for an off shore DP if I were planning to upgrade to one of those multiple times more expensive DP's at some point in the future.
