Hi Logan,
Generally windows does a lot of caching by reserving memory for recently loaded or frequently loaded pieces of data. This could anything from dlls to textures to whatever was in the RAM previously. So next time windows accesses a common piece of data it no longer goes to the harddrive but to the memory and loads it from there. It actually keeps it in memory which is many times faster than a harddisk and even an SSD. Windows does this even if that file is not currently being used, because it knows that you might want it again from previous usage patterns. Before we continue I just want to say that this is not a bad thing and later versions of windows seem to do it better and better. In general, if you are experiencing this type of issue, you should buy some more RAM, preferably double it. I bought 16gb of RAM even though most people say 8 is more than enough. The reason being is because when I did get 16gigs on my previous setup I immediately felt a speed improvement when I alt tabbed out of games into the desktop. It cant be too good for the game if your PC is already struggling to switch to desktop due to having to reallocate available space from your game to show the desktop and programs.
Memory cleaners bombard your computer with numerous request of high memory allocation forcing other programs to relinquish their reserved memory space and drop cached files in windows. They are quite aggressive and do a decent enough job of freeing up as much RAM as possible for the immediate improvement in some cases, but they might also put quite a bit of extra stuff into your virtual RAM which is part of your RAM being moved onto the Harddisk to be trickled back later into the real memory.
So yes, I would say it is safe to use them in general. At least I never ran into one that is dangerous to use, but you should really just get some extra RAM. I am glad it is helping you, that is awesome and I will mention it to others that stutter in games as a last line of defense.
Cheers,
Gabor