You are correct that at the time there wasn't many options, I believe they were all roughly the same price, and we didn't have enough data to say what was good or bad. I suppose the title and content of the OP was a bit emotional. What I was trying to convey is that, now that we do know the answers to these questions, and considering there are a lot more options, people can now make an informed decision. I would say this is a fairly tight-knit community of probably less than 100 active members on this sub-forum. Newcomers will look to our experience to make decisions. Sharing those experiences is critical to the community. I think most of us can agree that the KW V3, Redwood varieties, MPP varieties, and MCS varieties are all fairly proven on this chassis and which one you choose is ultimately dependent on what you are looking for. I also think the Ohlin's R&T will probably be a good option, and someone has pretty good chances rolling the dice on that one despite it technically being unproven.
I have purchased several Megan Racing products for other platforms. I do think that Coilovers are squarely in the not worth it category. Keep in mind that if people can't DIY these, they are probably paying near $1,000 for installation and an alignment. I would think they would be pretty unhappy having to pay that labor all over again in two years if the suspension prematurely wears out, which I am fairly confident would likely be the case for a set of MR Coilovers on the Model 3, especially in Northern climates such as the Coilovers in this post were.
However, if you're talking about something fairly simple and straight-forward such as control arms, that's not nearly as much of a concern. Labor costs are probably pretty minimal, changing them out is fairly painless. I can totally understand why you would do that.
Now, is it worth it - personally I would say no, not to save a hundred or two-hundred bucks, but that's just me based on my experience. I spent years trying to play that middle-ground of 'cheap but not complete crap' with modifying cars and when it was all said and done it caused me to spend more time and money that I had originally thought. Several times I ended up replacing a part that I thought would work out that didn't, either due to fitment issues, wear and tear, or changing needs. What I have found, in my personal experience, is that it is better to look at the long-term costs than at the up-front costs. E.g. if I decide to part-out and sell this car in three years to buy an electric Porsche Cayman, what are those control arms worth on the secondary market? If, say Redwood arms are $400 new and $300 used, but the MR arms are $200 new and $50 used, I would rather buy the Redwood ones. And of course, the warranty, customer support, materials (aluminum vs steel, for example), these all need to play a part in my final decision. I think it was you and I who were going back and forth regarding AutoX brake pads. My argument was, (and still is) that I would much rather put some RB XT-910's or 970's in there for $200 and save the stock Performance pads then to wear out the stock pads and be forced to pay $330 for a new set. Again, I'm looking at these things on a 3-year horizon, which I understand is not everyone's style or budget.
At the end of the day, this is a pretty crappy experience for the owner of these coilovers. Their options are few. They can pay to have the coilovers removed, send them in for a rebuild (hopefully covered by some warranty), and then pay to have them reinstalled. Or, they could pay to have these removed and just put the stock suspension back in. Or, they could ditch these and pay to have some other coilovers installed. No matter what though, it's a huge pain in the butt, and a pretty big expense. I believe it is important for the community to share when parts just simply don't work out. And I am not trying to say that we should never try new or cheap products, but we also need to understand that there is risk associated with that and there are going to be times where it ends up backfiring. For a lot of people, that's probably not a risk they want to take. Yet, to your point, we should probably be supportive of those willing to take that risk rather than dismissive.
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