Oh my, this thread is a gem. I don't know how I missed it until now.
As someone who has used CFOP until about sub15, and now averages ~9.25 with ZZ ( ~12 onehanded), let me give you my perception of the pros and cons of the method, when compared with CFOP:
Cons:
-While EOLine by itself is just as easy as Cross, and only like 1 move longer, it is significantly harder to plan anything after EOLine (tracking pieces of a 1x2x2 through seemingly arbitrary moves that solve EO is harder than straight blockbuilding for XCross) HOWEVER: EOCross is extremely easy to plan every solve and only adds 1-2 moves on top.
-L2/R2 moves are bad, and blockbuilding is hard and awkward. While a bit overstated, this is true (though only for two-handed) and it is why I nowadays believe EOCross is superior to EOLine, only for two-handed. You sacrifice some movecount for better inspection, easy lookahead and crazy TPS spam in F2L.
-RUL moveset in F2L is bad due to frequent regrips and slow LU. This is true, but can be a) mostly alleviated by solving the left block first (it has much fewer moves then and you get an all-RU-block afterwards or b) completelely avoided by using z-Rotations. for example, one could sovle the right block first, rotate z and solve another right block, getting to LL on what was originally the left side. Alternatively, one could just solve EOLine on left and solve the left block first with RUD, then rotate z' and solve the right block with RU. Since I struggle recognizing ZBLL on different colours and never learned to start a solve from Z, I myself often solve the right block first if it's easy and then rotate z to have a completely RU left block.
-The last slot cases are long and awkward. Yeah, since you have to stay 2gen, they are longer in movecount, but because CFOP ones often include rotations, they are often just as fast to execute in reality. 2 or 3 of these cases really suck though, without question. This is also why I advocate not solving 1x2x2s on each side and then doing essentially 2 LS-inserts, but rather finishing one side completely with blockbuilding before starting the other one. This reduces regrips and movecount.
-ZZ is not very flexible for use with other puzzles/events. I cannot understate this. ZZ is absolutely, completely, utterly useless for 4x4, and I would advise noone who wants to get good at 4x4 to use it. I myself have tried many ZZ variants for 4x4 and none of them come close to Yau+CFOP, even though I don't even know full OLL. It is not useful for Megaminx, neither for 2x2 (even though COLLs work as CLLs, they are not very nice to execute, and you might struggle with colour neutrality when coming from ZZ). ZZ can work well on uneven big cubes like 5x5 and 7x7, but that's about it
Pros:
-Extremely Easy lookahead. Because you always solve in the same one or two orientations, you do not have to be aware of where your pairs go - the same colours go to the same place everytime. There are also just plain fewer F2L cases because the edges are already oriented - this makes keyhole-cases which solve two slots at once extremely easy - you do not have to be aware of how the edge is oriented, there is always only one possible case.
-Nice execution due to no rotations and a lot of 2-gen. While rotations aren't that bad for twohanded, it's still noticeable and the long streaks of 2-gen solving are a dream. For onehanded, this alone makes ZZ much, much better than CFOP could ever hope to be.
-Many possibilities for last layer. Every alg you learn for last layer is insanely useful. From OLL/PLL over COLL/EPLL, winter variation, 2gen reduction, phasing + ZZLL all the way to full ZBLL, everything is worth learning and isn't just one random trick you might use in one of a hundred solves. While with CFOP, you can learn all these things and they might prove useful, it is hard to have a reliable consistent LL system. Full ZBLL will not be used on every CFOP solve, making the method itself inconsistent. I have learned all of ZBLL and just having 1 look and 1 alg on every solve is great and has dropped my times significantly. This also makes ZZ very interesting and anti-boredom. There's honestly so much to learn.
-Efficiency. If you do EOCross and ZBLL you are still at around 50 movecount, lower than the average CFOP solve. If you do proper Blockbuilding and ZBLL, staying under 50 is very easy. This again is great for onehanded.
So, to conclude: in my opinion, ZZ has a lot of potential. I'm not sure if it is better than CFOP for twohanded, but it's surely just as good. It doesn't compare to the god method Roux, though. For onehanded, ZZ is vastly superior to CFOP in absolutely every aspect. How some people think CFOP could be better than ZZ for onehanded eludes me. I used to think it's better than Roux as well, but I misjudged just how fast people could get at table abusing M slices. So I would still crown Roux the overall King Method for 3x3. (If table abuse were prohibited, though.....

)