It is one of those questions you constantly struggle with throughout any technical career: Should I learn this latest and greatest technology that is out? Do I need to learn it, do I want to learn it, do I get left behind if I don't? The truth is that you can't learn everything so how do you know what to focus on?
The sections below are not mutually exclusive, nor do you have to fulfill all of them. If you can say "yes" to one of them, then you are probably okay to invest time in the technology in question.
Is it core to your work?
If you are working on a project that requires a new technology either to complete a certain part, because the customer want to use it, or there's value in using it instead of what you normally use, then investing time in learning it makes sense. Sometimes you won't have a choice, as it is mandated by either you manager, or the project itself, but take this as an opportunity to push yourself.
When new technology becomes a requirement from your day to day job, it isn't a guarantee it will take off, but at least you have a low risk angle to learning a new tech. It doesn't mean you can't be critical about what you are learning and using, you absolutely should be, but it does mean you can invest someone else's time and money to learn and progress.
Can you make money from it?
Whether it is for your professional day job, a side project, or a freelancing gig, it is worth asking if you can financially benefit from learning a particular tech. This might not be a direct monetary payment, although that is an obvious choice, but it can indirectly benefit you. If you learn a technology you can later teach, consult in or sell as knowledge for a future project, this can also be worth your time.
There are many ways in which you can profit from a new technology, and there are equally as many you won't. When you evaluate if there is a financial gain, be prepared to ditch the learning if it proves invaluable or a waste of your time. I know that some people can't ditch a project halfway, as they feel they have to finish it, but then you just end up wasting more time.
Does it spark your interest?
While the first two points is really related to your income, either directly or indirectly, if something really sparks your interest, then you will most likely find time to learn it. In some ways this is the easy one, because focusing on something that is interesting and irks your curiosity is always easier. On the other hand, it is hard to stay objective and recognise when you should abandon it.
Although it can be hard to know whether to invest your spare time or not, if you have that passion for it to keep going, do so. There is nothing that can fuel your learning like genuine desire to know more. For many years I was extremely passionate about the Windows Phone platform, and even as its popularity and appeal waned I kept pushing and learning. It got me a Microsoft MVP title, and I spoke at conferences around the world. It opened doors that would otherwise have been closed.
Does it have future support from the makers ?
I have been burnt a couple of times by investing my time and energy into a technology or project, only for it to be abandoned. Granted, it isn't always obvious what will be a success and what won't, but if you look at the track record of the company or people behind it, then that is a first indication. Also, look for major projects the technology is used in and support statements from the makers. If, for examples, Facebook has created the core tech, then it is pretty likely it will be supported for the foreseeable future. There are other indicators as well: Is there an active support channel? Is there a general interest in the community? Can you envision a future path for the tech, or is one even published?
Do you want a career change?
Are you looking to change careers, field of expertise or explore what other opportunities are on offer, then investing time in a new technology is a great idea. But, which one should you focus on? We are back to the same original question, but use the points above to determine which and how. If you are after a change, it is up to you to facilitate it and take steps to make it happen.
Changing career paths is a whole other conversation in itself, but being focused on a new technology is a good start, as it will create a path for you. Whether it is a path that is focused on your passion, a new popular tech or advancement within your current company, a new tech can help you along the way.
Never stop learning
Regardless of your success in choosing technologies that are relevant and stick around, you should never stop learning. There is no equilibrium in technology; you either progress or go backwards. Picking a new topic to learn regularly is as crucial to your career as it is to exercise your brain. Some you will get right, some you won't, but they will all help in keeping your skills relevant and your mind sharp.