It's a year later and I don't see the expert's mode in current version, unless its hidden and I just don't know where to look. I'm using the .rarrc file to set solid as well as a number of other options, which I'd do anyway for use from the command line. However, it would be nice to be able to override these in the GUI when appropriate.

Also, I notice that when setting the compression mode, it assumes rar will operate with -m3 and so does not seem to specify it. If I have -m5 set in my .rarrc, I can't get normal compression from BetterZip, but can get faster (-m1) and none (-m0). If you just pass -m3 for normal then the selection in the GUI should always override the .rarrc and produce the expected results. This probably doesn't affect a lot of people, but I have my .rarrc setup for maximum compression to ease cli use.