Yes it is. Many make the mistake in saying, that the Enterprise (aka Commercial) version of dual licensed open source products is not open source. In our case, it is still open source, so you get the full source code, and you can do many things with it.
But why pay than? What is the commercial version for?
Because the commercial or enterprise version is a cleaned up version of the code, it is tested and proven. The community version (the free, unsupported) is based on the recent commercial, but contains many experimental or unproven technologies. It is still stable, usable, but some parts may be too risky for real enterprise grade operations. But it is this community code that is the basis for the next enterprise, and the cycle begins again, as the last enreprise is the basis for the new experiemetal developments...
What are you really paying for?
There is an old hungarian saying, which loosely translates "Don't you check the teeth of a horse you get as a present." So when you get something for free, take it as is. Many dual licensing vendors use the latin "Quid pro quo", meaning "something for something" to describe this model.
In our case, the paying version of dual licensing comes with legal protection (againsg infringment lawsuits), some degree of warranty (for high priority bugs), and profressional support. The degree of the protection and extent of support depends on which package you choose. Naturally, the more you ask for, the more we ask for. This is fair business.
So there is no version that is free of charge?
Yes there is. The other branch of the dual license is the free community edition, which you may use at your own risk, which is only supported by the community (which includes the developers when they have some time) and there is no warranty, you either wait for bugfixes or DIY. But this one is totally free, you are only bound by theterms of the GPL, which ensures that this version remains free source even in its derivatives.