It took them time. I had asked the same problem few months ago [0]. I needed a tool to subset a huge PostgreSQL db. The choices where Condenser [1] and this Jailer. Since I'm not a Java guy, I was struggling to know how to properly run this Jailer. I'm glad they released a .deb format. But I ended up using Condenser.
Java is a huge plus over Python for me, namely type checking and ease of deployment.
I don't know either jailer or condenser, but I know that jailer@java has an unreasonable better change to have less bugs then condenser@python. Like you already noticed, condenser produces errors during run time.
I just took a quick look at condenser application you linked. Only supports Postgresql and MySQL. This is often the case with none Java tools. They tend to support a select few number of databases. With tools that support JDBC you will be able to connect to most databases. That is often my challenge as someone who works in BI.
I don't know either jailer or condenser, but I know that jailer@java has an unreasonable better change to have less bugs then condenser@python. Like you already noticed, condenser produces errors during run time.