I think with some of these opinions there may be some confusion on the JBL model numbers - the 4425 is a two-way time-aligned studio monitor with a big "butt-cheek" constant-directivity horn. It has virtually nothing in common sonically with the earlier 43xx/L200/L300 speakers that use the slant-plate style midrange horn, or the 4310/11/L100 that have a cone mid/tweet.
Compared with the earlier slant-plate/cone-tweet designs, I can see how some would prefer the NS-1000 . . . personally, I'm not a fan of any of it. But the 44xx series is another matter - they're smooth and precise, with good imaging and a wide sweet spot. You certainly don't want to be too close (I'd say 6-7 feet minimum), but there's no getting around the fact that the directivity characteristics of the 4425's horn are simply vastly superior to the mid-tweet array of the NS-1000.
The 4425s standing by themselves might sound slightly bass-light in some rooms, as in studios they were frequently soffit-mounted. Bass control and extension is excellent. Keep in mind that in their native application it was not (and is not) frowned upon to use a light application of outboard EQ (in conjunction with the built-in EQ controls) to get them perfect.
But as always with vintage stuff, condition frequently trumps everything else. Most old studio gear was worked VERY hard, and sometimes repairs were performed on a tight budget and short timeframe. On the other hand, you'll also find equipment that is very worn cosmetically, but maintained by engineers that knew what they were doing, and sounds fabulous! Consumer-oriented stuff like the NS-1000s usually leads a very different life . . . and your comfort with the particulars of the sale is likely to be as important as the particular speakers you choose.