My Dullcote results have been the same all these years. I tried the Tamiya flat clear, but it just wasn't the same as Testors.
No doubt it is easy to get “comfortable” with Testors. I've used it from rattle cans in a 43-degree garage to in brutal sunlight on 95-degree-plus days and had zero problems. Same with it from a bottle thinned for airbrushing.
I would be using it right now, except my second bottle hardened up this summer after 3.5 years. Probably due to the room it was stored in had the air conditioner off over much of the summer.
That threw me over to using some Tamiya XF-86 I have on-hand, and thus far I find it as reliable and flat as Testors dullcote.
I do find that the Tamiya, being alcohol-based, doesn’t suffer clogging or tip drying as much as Dullcote, which is a lacquer.
But on balance, when I run out of the XF-86, I can see myself going back to bottled Dullcote, but really for cost considerations. It takes roughly five bottles of XF-86 to equal the volume of one bottle of Dullcote.
But then again, it’s not that cut-and-dried - if I stock up on Testors, shelf life might bite me and eat up savings.
Also, lacquers can more readily attack prior coats of paint, because lacquer thinners are stronger solvents. But I haven’t had problems with that myself (well, yet).
Now I’ve made myself curious - I still have my dried-up bottle of Dullcote - I’m going to see if I can revive it by pouring in some lacquer thinner.