In case you did not know, the Excaliber comes in 3 sizes - 16", 21", and 30". The EX-16 has had some vibration concerns posted here. The EX-21 with a stand (I have one myself) is very stable and easy to change blades. I have not tried the EX-30 but I'd expect the added weight of the big table would further reduce vibration. So vibration-wise they go from not-so-good (16") to exceptional (30") - you need to know which one you're looking at. Similar with the RBI - there are different models. And note that RBI shut down, then re-opened recently. Check parts availability for the CL model you're considering.
Also note that the Excaliber has a tilting head with a large protractor adjuster below the table - rather than a tilting table like the RBI. I find the tilting head easier to use when cutting at an angle for bowl or basket work.
RBI has a unique feature - you can change the forward leading angle of the blade - increase the angle to get a more aggressive (faster) cut. I don't think I would use that feature - I like to cut very slowly - and I suspect it would not be much benefit to a newbie scroller.
I fully agree that you need to try any saw you consider on CL. If the owner will not let you try it for 10-15 minutes or so, or show how to change blades, adjust angle, etc., then forget it.
These machines are not that simple - lots of bearings, levers, and odd motions - so I would recommend buying a new saw from Seyco or RBI and getting the assurance that it will work as advertised for a long time, and have parts available when needed.