SymmetricDS is a bit scary for a first timer in the world of databases. It has two major things going for it: 1. Excellent support from the developers, and 2. Very complete documentation The documentation is rather long winded at times, needs more examples, and in some cases conveys different meanings than was intentional. However, given the support from the devs, these are minor complaints, and I think SymmetricDS has a bright future.
Can't speak for the command line version of this product but the web based solution from JumpMind is a mess. Very flaky software. Full of bugs. Cannot handle volume as mentioned. Tried pushing through thousands of batches and it just fails miserably. Correct updated documentation is nonexistence. Good luck trying to figure out how to setup the software. Very hard to get a smooth working setup installed. Trial and error seems to be the way they want you to figure it out. Unless of course you shell out money for consulting fees and any real technical support. Also when trying to evaluate the software, got nothing but sales pitches to buy consulting technical support. Very disappointed with the product. Not at all like the site touted.