It's better than Progressive. It's quite good, in its way. One can actually see the point in it. There's some worthwhile stuff here and I tended to find the episodes interesting and worth watching.
Personally, though, I think the whole project was a bad idea. Why make a sequel to FLCL? Why, why? A sequel is a continuation of the original's story, but FLCL ended up as stream-of-consciousness mental anime-squared that wasn't trying to be intelligible. (Its early episodes made more sense, though.) It was impressive, but deliberately trying to break the rules of anime. Its director, Kazuya Tsurumaki, replied to criticism by saying that "comprehension should not be an important factor in FLCL".
That is not a foundation for a new story. Trying to make it into one will result in a building that falls over. This project was always an example of dollar signs trumping storytelling. A plot synopsis might go as follows:
Original FLCL = random + "What the hell?"
FLCL Alternative eps.1-5 = four likeable friends goof off and make life mistakes
FLCL Alternative ep.6 = the show remembers that "oh yeah, this was FLCL, wasn't it?" Good luck trying to find explanations for what happens in here. It's cool, though.
In other words, this starts and ends with wackiness instead of clarity. Personally, I thought any success here was in spite of the FLCL elements, not because of them. Oh, look, it's Haruko again. (She's fun, but she's basically a walking surrealism machine, not a dramatic participant.) She's still hitting things with her guitar. Well, well. Apparently this was planned as a prequel, not a sequel, but I can't say I cared about that.
As well as all that, though, we also have good times with Kana, Mossan, Hijiri and Pets. These four schoolgirls are rubbish at life and liable to lash out or get protective about the wrong things, but they're not going to let that stop them. It's called being a teenager. Hijiri's a model and her episode's all about being a kid, a grown-up or someone who's pretending she's better than others by being a grown-up and looking down on them. (Haruko pops that balloon.) Mossan is indomitable. Kana discovers (a) boys and (b) the art of pulling comedy faces. Then there's ep.5, in which harsh things are said... which, on closer inspection of what led up to them, are painfully justified.
Also, in fairness, all that FLCL wackiness is fun. Unlike Progressive, the characters and story are strong enough to anchor it. You've got a skyscraper-sized iron, impossibly sprouting foreheads, the rich migrating to Mars, the Hand of God and possibly the end of the world. Also, Haruko.
Is either of these 2018 FLCL sequels worth watching? Not really. I'd have given Alternative a recommendation had it been divorced from FLCL, but Progressive is a dead loss. On objective measures, though, Alternative's quite good. Decent stories told with an interesting cast. It's quite fun. By all means watch it if you don't mind a story that's probably a sequel or prequel or something, ends in opacity and has plenty more opacity sprinkled along the way.