I have been using it on my mid-2011 iMac (16MB RAM and 256GB SSD) for few months since version 3.3.5. Other than small hiccup during transition from version 3.3.6 to latest version 3.3.7, it has been running smoothly and transparently without any issue (you can quit and restart it just like any other applications without affecting operation of Mac OS X). I bought it through Apple's Mac App Store, I have to create a Unix shell script to replace it temporary when version 3.3.7 was not yet available in Apple's Mac App Store. Standalone and trail versions are available at developer's website as well.
I create a RAM disk of 800MB and mount it at Caches folder under user's library folder to redirect all read/write access away from SSD to the RAM disk. As long as the size is under 1GB, it can be created within kernel memory (so called wired memory) thus it will never been swapped out to disk by paging operation. I notice speed up of many executions of applications include browsing Internet in Safari browser. The size of 800MB is more than adequate for most applications (more than twice the size of original Caches folder on SSD). As long as your Mac is installed with at least 8GB of memory, memory foot print of iRamDisk is really negligible.
With its small memory foot print and low price, I find it is money well spent as iRamDisk is a more elegant and transparent solution that Unix shell script. There is nothing wrong in prolonging life span of SSD even though it outlast life span of your computer, just take it as good side effect rather than main reason to use iRamDisk. Install the trial version and see the effect for yourself, there is no risk involved as you can quit the utility any time and everything recover back to original state. Of course you have to use your discretion to decide on proper size of RAM disk based on available memory, otherwise only your stupidity has to be blamed for frequent paging (common sense and practice of computer engineering).
It is most beneficial for notebook computer with slow hard drive (5400 rpm) and low battery capacity as accessing memory take much less energy than accessing drive even for solid state drive.