I've worked with different RAM expanders in the past, and what I can say is it all boils down to the SPEED OF THE MEMORY you want to make use of, if it's your SD card then you'll need an original version that has up to 13mbs read /write speed to make this app work effectively else it'll be very slow, and it works by creating a swap file on your preferred memory that swap file is similar to paged memory in windows it pushes common idle activities that take up memory to the file when your memory gets low so when you run that same activity as main it pulls it back to main memory, it does not use your SD as ram (as this would quickly spoil your memory card) because SD cards are much slower than RAM.. So having 4.5gb of extra ram is nothing if you don't have an original SD card that has enough speed to make the swap

And I forgot to mention, you'll need to grant root access for this app to work