Windows 10 Mobile will never "be finished", it's an OS that's constantly going to evolve.
The production ring that will be installed on the 950XL should be fine. It's only when you get impatient and join the fast ring where you have to go through some ups and downs.
That's actually not entirely true. Windows 10 was released early to gain market share. The vision for Windows 10 being finished is redstone 2. Now after redstone 2 once the vision has been reached it will constantly continue to evolve and features will be added. But it is definitely not finished. It's a slow process they are working on while getting feedback from users. Redstone 2 will have the full control panel settings moved over to settings. All the features they planned already will be put into place and then they will work on enhancements. So I see Redstone 2 as Windows 10 being finished. Then the evolution of windows 10 will continue from there.
And to the original poster. I'm happy with my 950XL. Initially there were lots and lots of problems when I bought it. In fact, it's only now that it has become stable enough that I could consider it a product that MS can sell. I knew what I was getting into of course when I bought it right away. I did expect it to be a little more fine tuned but hey, it does what I need it to do.
I think that if you aren't very app centric then go for it. But if your friends use apps that you like to be a part of then go for iPhone. You will not get snapchat on here nor should you expect to in the future. More apps are coming out no doubt but you will likely still come across a scenario where you may not find an app that you wanted to use. There are some great third party alternatives for things like tinder, reddit, etc. Twitter and facebook are there. Most of the big main ones are available. They are not quite on par with the ios equivalent but they seem to be getting worked on. I use Line a lot and am happy that they have a windows 10 app that they are constantly updating. Twitter app is awesome, I actually prefer it to the ios one. Facebook currently will let you do the basics but is not as feature rich on the phone. Though there are plans for this one to gain parity eventually. Continuum is great and once you really experience it you will actually see the huge potential. The only issue is that edge is super slow in continuum. I think that once extensions come with adblock it will speed up quite a bit. Even the desktop version was super slow but with adblock being added recently I'm actually using it as my main browser with no issues.
It is definitely a work in progress and the insider builds do show it getting better with time. But while the OS may get better don't expect the app situation to ever be on par with ios. It's looking more positive at this point, but you can't rely on that. Just because there's some motion no doesn't mean it will continue.