If you think having two DNS providers is a hassle then you are probably doing it wrong — if you setup a hidden primary configuration then adding an additional secondary is just a matter of giving the new provider your zone name and IP address and then updating your delegation.

In case you're not familiar with it, a hidden primary configuration is just a master setup to allow zone transfers with the zones themselves not including a delegation to the master. This means the only queries your master serves are zone transfers requested by the secondaries.