I have Jolla phone and I have mixed feelings about it. Sailfish OS is interesting - learning how to use it has steep learning curve (but once you get used to it, it's perhaps faster to do something with it than on any other phone). It is sometimes unreliable (my Jolla randomly shuts down, sometimes several times in a row, see https://together.jolla.com/question/7144/jolla-randomly-shut...). There are other quirks here and there, guys from Jolla are fixing them one after another, but I would say that Sailfish OS is still in beta state.

It is really developer friendly device. It has awesome SDK and it isn't trying to restrict you by any means. But even that, there are not really that many applications for Sailfish OS and only few of them are good. And there is literally no official client for anything and that brings problems - for example, several people were banned from WhatsApp for using Mitakuuluu (WhatsApp client for Sailfish OS). There isn't full-featured Facebook client, there isn't client for my bank account or for my operator. App for public transport for your country? Nope, it isn't there. Sure, you can use Android apps (not from Google Play though, you have to use Yandex store or Amazon store), but: 1) There are no Google Play Services - that means no integration with Google Account, no maps, no that pretty cool Google Inbox app, Google is moving a lot of things into Google Play Services, 2) there will be problems with any non-trivial app. Games are OK, but GPS tracking? Didn't work when app wasn't active (so you have to have screen on). Wanted to try Pressy? Doesn't work, it wants to access your Google account. Besides, if you are buying this device convicted that you will use Android apps on it, why not buy Android phone?

To end this comment with something positive, I could say that this is "OK" device. It is impressive that they are able to build this device with that small team. They are listening to community, they are updating their OS frequently. Besides some quirks, Sailfish OS is as good as any other mobile phone OS. It runs fast and it is based on Linux, Qt5 and even Wayland compositor. You can be more confident that you are not being watched (at least they say). Your inner geek will be pleased. But at the end of the day, you will look at other people phones, they are playing that new cool game, using that new cool app you always wanted to try, trying that new HN or Reddit client, using Google Inbox, using Instagram Hyperlapse, using their expensive gadgets, fitness trackers, using their phones to find how will they get home and your phone has just suddenly rebooted again.