Cool audio panel - if it only worked
I bought the audio panel and marker beacon combo back around mid-2003. I do not recall having any issues with delivery times back then. The kit is very nice and well documented. I would note however, that the boards are very densely populated, and I would hesitate to recommend the kit to someone with limited soldering experience.
I assembled both units and they passed all of the tests as outlined in the manuals. Unfortunately when I installed it in the plane, I had some nasty audio feedback when I keyed the mic. In addition, there was quite a bit of "crosstalk" between the audio channels. I initially thought this was an RF problem, however I reproduced the audio squeal problem with the unit on the bench outside of any RF influence.
After a few technical email exchanges with RST, I was told that there were a small number of units in the field that exhibit similar problems, and that he did not know what the exact cause was. By this time however, I had decided not to add a second radio, and wired up my SL-30 to use its internal intercom. At this point, I put the audio panel and MB in a box to collect dust, and they sit on a shelf to this day.
I think if you were lucky and got a "non-squealer" unit, or were savvy enough to debug one, you might have a pretty nifty audio panel. Heck, I might even try to resurrect mine someday. If you are looking for minimum hassle however, I would not recommend RST based on my experience.