They are expensive, and the upfront price is only scratching the surface. Add the consumables and accessories needed and you're at 2x's the original price or more. It's tough to justify, especially when there are so many other options on the market.
But there are a few areas where I think they excel.
1. Dust collection - the tool companies have long ignored this, and slowly people are becoming more aware of how hazardous inhaling sawdust can be. I suspect in the next 10-20 years dust collection will not be a feature, it will be the norm. Meanwhile, every one of their saw dust tools can be fitted with dust extraction using standardized port sizes. You don't need to cobble adapters together to make things work. You pay for this.
2. Portability and space - Their tools designed to travel, as such, you can find ways to do most things with them that you might ordinarily do with free standing tools. If you don't have the space for free standing machinery, Festool might be able to fill the void without taking over your entire shop. It's not necessarily cheaper than the stand alone tools and sometimes it takes more set up time and creativity, but you would be surprised. You pay for this.
3. Ecosystem - some of the tools are designed to work together, so are the accessories. Take the MFT...it's a worktable (an expensive one), a clamping table (an expensive one), and a cutting table (an expensive one). Using the grid pattern and a few accessories and the track saw you can make dead accurate 90 degree cuts. If you had the extensions for the kapex miter saw, you can also put them on the MFT for outfeed support. Or buy another MFT table and join them to have a bigger (more expensive) table.
4. Quality - they are built better than most power tools out there. Their engineers look at a tool and ask how they can make it better, where other companies seemed more focused on how they can cheapen a product without it going noticed. You pay for this.
5. Precision - Their tools are designed with a craftsman in mind. Need to move that dado 0.1mm over, no problem! You pay for this.
If they didn't have a place in this world because they priced themselves out, they would be out of business. The truth is, they are doing quite well, even on this side of the pond where we insist on using imperial measurements. There must be something to their tools. If you have an open mind and are willing to try a few of their tools, you'll start to see how they can make your life easier. Yes, I drank the kool aid 8 months ago when I got the track saw and dust extractor. I hmm'd and haw'd over the purchase and finally decided I just wanted to get a job done and this would be a good test for it. I still struggle with each additional purchase, right down to the drill - a purchase I will admit was an indulgence, because it's just a drill. Even that surprised me! I can modulate the speed and power through the trigger better than any of my other drills. Final torque on every screw was always done by hand, because I never felt a power tool gives you that precise control. The C15 drill changed my mind. I'm gonna pay for that. You might too.
The single biggest drawback, in case you hadn't picked up on it, the price. The second, that price creates very high expectations. Has Festool disappointed me, sure. But I tend to criticize them for things I would never expect of another tool manufacturer - "if I can have a micro adjust on the bevel, why couldn't they give me a micro adjust on the miter???".
So that's my spin on it. If you have the luxury of setting aside price, give their tools a try. Don't just hold them in the store, take 'em home and give them a workout. If you're not happy, send it back. If you are, then wrestle with the price and whether there is still value in it for you. Nobody on some internet forum is going to answer that question for you, it's something you have to figure out for yourself. That's my $0.05.
