I really love the graphic images in the LnL rulebooks, but ultimately I prefer the clean design of the THW rulebooks. With all the whitespace and large margins, I can pencil in errata and reminders as needed. For example, I've penciled in the two Citizen Brown Pants rules' page numbers in the appropriate pages of the QRS so I won't forget them. I also have a comb binder, so I've printed the updates posted in these forums that I've inserted into my rulebook. That's the main reason I haven't purchased the LnL books. "Nowhere Nevada" was very tempting, even though I already have "Haven."
It's difficult for me to gauge which rules I use from FFO, which from the updates (I know the change to the melee rules against zombies introduced in "High Moon" and found in the update is one I immediately adopted), which from the supplements such as "Tales of Dread," which from the updated mechanics found in other THW rules, and which rules I improvise myself (Such as my test to see if phones, internet, and electricity are available during the initial weeks of the outbreak -- roll 2d6 vs. Week #, pass 0d6 = operational, pass 1d6 = out of service for the current encounter but can be tested in next to see if comes online, pass 2d6 = permanently out of service for the area). I suppose an ATZ update wouldn't be such a bad idea to pull things together the way it was done in Nuts, though you probably won't need to have a separate compendium.
That toolbox aspect works the other way as well, as I've used ideas from ATZ in other THW titles, particularly the random event rules that I sometimes create customized to whatever encounter I'm playing. In fact, I've often thought it would be interesting for THW to produce a booklet devoted specifically to various tools that have potential to be used across a wide variety of genres ("Chain Reaction Compendium" or "Advanced Chain Reaction" perhaps? Though it shouldn't be a free product.). For example, THW used to feature rules for building interiors in an earlier version of 5150. Such a resource could also feature some of the earlier methods of the rules for those of us who don't mind the extra level of detail and dice rolling. For example, the earlier method of resolving In Sight based on individual characters rather than groups is thematic in non-military settings such as the wild west or even the zombie apocalypse. As a matter of fact, "Chain Reaction 2015" preserved the weapon impact rules as an option for those who want it. Then again, resolving In Sights by group leaders is far less complicated to explain, so the modern mechanics definitely have the advantage in terms of streamlining things.
And I'm rambling, so I'll wrap this up...