So incorrect in so many ways.
Known to be problematic, and they only cache frequently used files, not everything, so if you have a large file that's not in cache it's no different at all from a regular hard drive.
One old firmware last year, now long gone, had problems on SOME machines. Current drives ship with SD28 or newer, which runs perfectly.
Even without the SSD caching, the drive is still the fastest 7200rpm laptop drive available. With the SSD cache, it far outperforms any other mechanical 2.5" drive.
If the drive was no good, why are Dell now fitting it to laptops, desktops AND workstations? Yes, a £5k workstation can be specified with a 500GB Momentus XT as a boot drive. Dell are confident enough to put the drives in their workstations, then there's really nothing wrong with them.
I have one in my MacBook Pro, it's been faultless for over a year. I'd have one in my Lenovo, only for the fact the Lenovo takes 7mm drives, and the Momentus XT is a 9.5mm unit. I also have the Momentus XT in 500GB form in a dozen Dell workstations at work, all doing heavy Adobe work, again with no problems. They're working out to be faster than the WD Velociraptor 300GB drives they replaced, too.
I take it you've never owned a Momentus XT, and are wrongly regurgitating outdated internet folklore.
The fail is massive in your post.