I actually have a Cinitq 24HD. I got it on the cheap by not sleeping with someone (that's a story for the not-art section). And it was the best investment of my life - things are much easier and much more natural, and I struggle a lot less with transferring my skills from digital to traditional media. If you are interested, have a quick look
at the art summary I did in 2014. You can literally see the month I got the Cintiq (November) - obviously the tools/brushes/fancy screen doesn't make the artist, but if you got the skill, it will amplify them.
I have not used any alternatives, but so far I believe Wacom has a patent on the magnetised system that the pen+screens use which is what sets them apart from battery operated pen+tablet systems. You do notice the difference; I have used both and by far prefer the magnet version to the current based one. If there are alternatives that use the same technology as Wacom tablets let me know I'm looking for one for a friend.
I do not know how well they synergise with Apple products; I have only ever used mine on a Windows OS and it has worked fine. Given Apple is supposedly the "artist's medium" in this digital stuff, it had better at least fucking work. It works with all of Adobe Creative Suite, Sai, and Manga Studio. Mine does not like FireAlpaca but that's more due to me having issues with my pen than the Cintiq itself.
My general summary is if you are super fucking serious business art is something you are sinking hours a day into, or you have a spare two and a half grand go for it, you really won't regret it, but is it necessary? Not really. Intuos tablets have all the functionality you need, and then some - it's a lot of personal choice and circumstance.