Alternatives to SQL Server TDE
We have quite some mixed servers, using encryption, depending upon the need of business. For very critical servers, we decided to upgrade to Enterprise edition as it not only provides TDE but other benefits as well when it comes to performance or troubleshooting.

Yes, TDE is quite effective and very good, but since it comes with a cost we decided for medium and low priority businesses to use a third party tool like NetLib.

I would like to highlight a few of its benefits, per our usage:


Provides Transparent Data Encryption and Column Encryption for all
versions of SQL Server from 2000 through 2014, and for all editions of
SQL Server from Express through Enterprise. SQL Server's TDE is
available only in the Enterprise edition of SQL Server 2008 and
later.
Easy to set up and maintain. Took us hardly 5-6 minutes to do so,
once we were aware of what needs to be done.
Database keys are stored outside of SQL Server, including alternate
locations such as network, removable media, etc.
Encryptionizer's Transparent Data Encryption has virtually no impact
on database performance (&lt;1%) on a properly sized server. Some
benchmark reports show SQL Server TDE to have greater impact on
performance between 5-10%.
Support for FILESTREAMS (SQL Server 2008 and SQL Server 2014).
Supports SQL Server Compressed Backups (WITH COMPRESSION).
Possible to encrypt system databases including the master database and the tempdb database.


I have not heard much about DbDefence, but yes I believe it supports Replication, Log Shipping and Mirroring. Read here for more info.

I believe you can have a trial of the above products and decide as per the business needs which suits your environment the best.