Not so short answer: If you want to learn something that makes you more marketable, then no. It is better to learn C++ instead. If you just want to play with it, maybe write an extension or two for your project, then Zephir is fun language to learn.
I checked for jobs dice.com and other popular job sites and I found 10 jobs on all of them combined. This is 10 jobs for both Zephir and Phalcon combined (searched separately). There are no popular websites I know of, that use Phalcon. There are some Russian and Polish websites that use it and I don’t know how popular they are but none that I have seen in the US.
Phalcon is the fastest framework but it hasn’t been widely adopted. In fact, I don’t know of any site, or web app that uses it. For those that don’t know: Phalcon (a PHP framework installed as any other PHP extension) is written in Zephir.
At first, I thought the lack of adoption of Phalcon (or Zephir) was because it lacks a wide variety of features (data mapper pattern being one of them). While that is true, that is not the only reason for it. Most websites (or web applications) run on shared hosting. They don’t have the ability to install custom extensions. So, unless the web hosting provider already has Phalcon installed, you are out of luck. This reduces Phalcon’s demographic by a significant percentage.
I think Zephir’s usage is directly proportional to Phalcon’s usage. As far as I can tell, it doesn’t seem very promising. One day when PHP let’s you install extensions like we install libraries through composer, it will have a better chance. For the near future, however, there are few to no job prospects for it.
Zephir (like its makers point out) is not a general purpose programming language. It was made for a very specific purpose of developing Phalcon and overcoming the adoption barrier. It is a bit limiting and expressing complex problems in it can be difficult. However, if you can get the hang of it, I think it is worth checking out.
On a side note: there is an app that converts your code to C++, making it compilable. It is called Swig and can be found here: http://www.swig.org”