Sigma FP is the successor in spirit to the Canon 5d III with ML. For one, the Cinema DNG files are unquestionably special; red raw is the only other codex that gives you such good color quality (subjectively, but I have worked with almost every camera in the past 15 years).
But the 5d has some serious limitations, such as true full frame raw (despite the fact that I enjoy the bullshit pixel binned 5.7k anamorphic setting), and I had issues with sound recording last time I used it. There’s just some hardware limitations, period. Fun to tinker with of course, and if you’re carrying it anyway, why not use it?
Because it’s now pretty heavy and also not low profile considering the options. Such as the Sigma FP, which fixes everything pretty much. Rock solid reliability, 4k cinema dng 12-bit raw, etc.
That being said, the FP still can’t shoot internal 4k 12-bit raw, requires rigging, lens adapters, ton of media storage, has a completely shit screen, you need to buy an expensive EVF, and without AF and stabilization you have to find solutions for those. So at that point, why bother with the hassle?
These are all just tools, and I’d say 5d iii and sigma FP would be suitable for art private projects or short films. I don’t think they’re even good for travel. IPhone 15 pro far more functional. It would have to be in very controlled situations, for any budget.
But as the production gets bigger, the cost to rent or buy between these cameras and that for a more pro camera is really not that significant, which is why nobody uses them.
Don’t waste your time and money, in other words. Buy the newest smartphones for private use. Rent the right cameras for work.