If you do try one, the following routine will be helpful:
Find a mid distant planar facade with detail.
On a good tripod with delay and MUP, shoot a sequence at 24mm, 28, 35, 50, 70, 100, 120 and at each focal length F4 F5.6 and F8.
For each combination of focal length/aperture, shoot a couple with Live View AF and a couple with Live View magnified MF.
Choose the best shot from each combination and look particularly at the edges. I don't mind if they are soft-ish at F4, maybe even a little soft at F5.6 but by F8 they should, at 50% on screen, be reasonably good and they should (but probably won't be) symmetrical. If they're not, see if you can live with not only that but also the way the DOF zone is skewed across the frame. I personally find that effect far more disconcerting in a final image than I do the soft edges.
If you can live with what you find, quickly check that the required AFFT at 24 and 120 are no more than 5 points apart. It will probably pass this test.
If all the above is acceptable to you, you will have an incredibly useful lens. I wish I could find one! It really is so, so useful and also very sharp on centre. If not, 'do a Jack' :toocool:
What might be of interest is I tested out a bunch of these lenses (the 24-120 f4 VR) with very in-depth testing shortly after they were first released. Three different distances at all major f-stops and all major focal lengths. Most every one had issues, especially fairly extreme asymmetry at the wider focal lengths, with extreme softness on one side of the frame or the other "especially" between 35mm -50mm. There was evidence of corner smearing too, although it should be noted that at 24mm, it was good across the entire frame. Zoom in a bit and the image quality would deteriorate. Images at the longer end of 85 and 120 weren't all that impressive either. The one thing consistant was that all these sample performed in this fashion. At the time, you could say I was not enamored with the lens.
Fast forward to the present and I once again tested a newly arrived batch these past few months. Clearly something has changed. Almost all the samples were now weakest at 24mm, with a small amount of asymmetry seen but at f5.6, it was just about "good" by f5.6 and by f8, nearly perfect in terms of consistancy across the frame. Of course with this lens, center sharpness is always of higher resolution than the sides/edges. At focal length of 27mm and above, no real evidence of asymmetry and performance was head and shoulders above the early batch of lenses. Gone was the extreme "one side" softness between 35-50mm, and performance from 27mm on up was quite good and often times a bit better than that, especially when the lens was used at f6.7 (which is close to the optimal f-stop in terms of even sharpness across the frame). Center sharpness though exceeds side/edge performance with most any setting.
Distortion, of course was (and still is) prominant in this lens, easily correctable in most cases.
This lens was clearly better than other incarnations of Nikon's similar lenses in years past, where it developed (and rightly so), a terrible reputation and left a bad taste in most peoples mouth.
The current 24-120 f4 Vr when first released may have been a much improved lens but it still had it's issues from what I saw in testing.
My theory is when Nikon was developing the D800/e, they wanted a alternative lens to the 24-70 f2.8, that people could use on that camera who might have desired a wider range or walk around/travel lens...so to speak. My belief is the early released version wasn't good enough to recommend for that camera and they apparently tweaked the 24-120 f4 VR and/or upped the QC in the process so that they would have a zoom of this type that they could include on their recommended list of lenses that performed well (or well enough) on the D800/e. I'd say in some respects, they achieved that goal from what I saw of recently tested samples. I couldn't say that before with the earlier samples I tested.
Whether it was simply a batch that had better QC or some slight changes were made in what portion of the zoom range they optimized the lens for, I can't say...but at least it was a step in the right direction. Is it equivelent to a top performing sample of a 24-70 f2.8 lens in that range...no...but it has other advantages as Tim, Jack and others have pointed out.
Dave (D&A)