My ZM Mustang arrived yesterday and I suppose that I got a different animal from the original poster. Here are my personal observations of my kit (your results may vary)
There is a COPIOUS amount of fiddly-bits in this kit. I've got a few kits under my belt and awards with some of them, so high parts counts don't intimidate me. That being said, unless you are going to leave the skin off of this kit, there is a LOT of detail bits and bobs that will be hidden once you zip her up. Also, after my initial review of the instructions, unlike the Tamiya kit, it appears that you can either display the engine access panels off, or put them on (which requires leaving out parts for the underlying structure. It does not appear that the panels can be, as designed, put on or removed at will. Not a ding necessarily - just a casual observation. Mind you, I was reviewing the instructions just briefly after an exhausting day - it bears re-look.
On the kit I received, the molding is noticeably softer than in the Tamiya kit. The panel lines remind me of the first generation of Revell US kits that had engraved panel lines. Holding the Tamiya kit side-by-side with the ZM kit ( I have both), You'd have to be blind not to see that the Tamiya panel lines are sharper - noticeably so. The parts molding overall seems akin to Monogram 70's era moldings. Yeah, there is a lot of detail, but what detail there is is softer than Tamiya.
In my kit, the main wing skins were in the top bag. I pulled it out admired that the exterior-facing side wasn't covered with rivet-divots, and then turned it over to look at the interior side. GASP! The molding on one wheel well was nice! Sharp and well executed. HOWEVER, the other side was soft and the reinforcement ribbing was barely there. Post-shading with a wash will probably make it pop out, but that's not the point. The quality of molding relief of the wheel well interior molding is different on each side - painfully and obviously so.
Now, all that aside: 1st-look pros and cons compared to Tamiya.
Mold quality - Tamiya wins hands down. It's sharper...more refined. Even though the rivet detail is given on the wings, it is restrained and would all but disappear after a couple of coats of primer and paint. Do like the real P-51 builders did - spackle the rivet heads then sand it down. Done. I plan do use Mr. Surfacer, then wipe down with Iso alcohol so that the filler stays in the unwanted rivet detail.
Parts count in comparison to viewable detail - Its' a draw per user preference. If you want to build one zipped up, buy the Tamiya kit. If you want to show the guts, go ZM. Still, Tamiya gives you a really nice level of detail... typical Tamiya - nothing to be ashamed about. One thing I did find absolutely stupid on the part of ZM is the inclusion of pistons and pushrods in the ZM engine molding. The engines on the ZM kit is a beaut, but what a waste of plastic. The pistons and pushrods will be hidden once you glue the two halves of the cylinder block together. If you got a clear engine block and separate pistons, that might make sense for those wanting to let it all hang out.
Instructions - ZM wins. They are beautiful, but Tamiya's gets the job done. I do have to note that yet again, a Japanese manufacturer only gives Gunze color references. Bad business. If you sell globally, you need to include color charts for Tamiya, Model Master, Vallejo, etc.
Decals - ZM wins...sorta (both give three schemes, but ZM seems to have more stencils, etc. on their sheets, which are larger, btw, than Tamiya. Still, Tamiya's decals are doable. Many will go for thinner after-market decals anyway - makes a huge difference when building a natural metal bird.
Variants - Tamiya wins on some, ZM on others: For instance, ZM gives you the three different canopies used by the D, Tamiya only one. On the other hand, Tamiya gives you both paper tanks and metal tanks as well as a separate tail to do the early D with no vertical stab fairing.
Extra bits - The one thing that shines for me is that Tamiya gives you both a seated pilot and a standing pilot included in the kit. Even though the ZM kit is less ($80), if you add these figures to your cart, you are going to spend about another $40USD. Now we're up to $120USD. I paid $125 for my Tamiya kit, I already get the figures included, and I get the options of different drop tanks and tail feathers. Another neat feature of the Tamiya kit is that it comes with a stand and is engineered so that you can either put the LG on and set in on it's wheels, or remove the components via screws, replace the parts with the gear-up parts (also provided) and display it on the stand. I like that option.
So, after a quick run through both boxes and knowing what I know now, I would buy the Tamiya kit over the ZM kit I if I wanted the best-looking static model of a 1/32nd scale P-51D. I would ONLY choose the ZM kit if I wanted to leave the skin off and show off the guts for the sake of showing the guts. For me personally, knowing what I know now, I would pass on the ZM kit. ZM has more parts and detail bits, but Tamiya is a better molding hands down.
That being said, since I have both, the Tamiya kit will be build to be what it is - a showcase standard for this beautiful steed. The ZM kit will be built so that one side is zipped up and fully painted with all stencils, markings, etc. and the other side will be left totally open for the world to see its' naughty bits. And, in the end, I guess having that option is the only place where ZM truly wins my vote.
I may have missed somethings, and like I said, this is just a first look. These opinions are just that - opinions, and are not necessarily the opinions of this channel. I now return you to your normally scheduled programming...
Cheers