I have Cara 2.2. Be aware that Cara 2.2 does NOT model Martin Logan's hybrids very well at all. The ML full-range planars are somewhat better, but not well represented either.
The problem is that MLs have several features that are difficult or impossible to model in Cara, such as curved panels and "Force Forward" woofers. There's something else about ML's design that isn't handled well, too, but I can't remember precisely which thing it was. This has been confirmed by both Rives and the original vendor, incidently.
It looks to me as if some other planars would be just fine (Innersound, Magenpans), and it certainly seems to have everything you'd want for modelling most box-style speakers. (Offhand I can't remember anything that would account for stuff like Omnistats, or the "eyeball" tweeters in either B&W or KEF high end speakers, though.)
Finally, be sure you get the 2.2 package. It comes with a tutorial, which is essential unless you're already an acoustical engineer. In my opinion, if you don't have the tutorial, you will find this software extremely difficult to use. The tutorial does NOT come with the 2.1 package, and even though you can upgrade your code to version 2.2 for a free download, that download does NOT include the tutorial, which is another $25 (ie 50% more). I should add that I found the software *very* *difficult* to comprehend, especially before I got the tutorial. It's NOT because I don't know my way around software, or CAD software in particular - I work in the computer industry and I use other types of CAD all the time.
Once you understand where you're going and what the basic orientation of the software is, the modelling is very thorough and seems pretty accurate. Unfortunately, since I'm a ML owner, it's only helped a couple of my friends who have box speakers.