I'm using Curtains to apply transparency with blur (Acrylic, standard, or basic) to File Explorer windows. (If I'm reading your question correctly) Minimal system resource usage, active right now with only 1.1MB of mem in use. Only thing missing is title bar transparency (It can be done with Curtains too, however, I haven't created an acrylic layer with gaussian blur to be applied to it yet.) You can apply transparency by way of a transparent .png from the start, I just haven't had the time to create one with blur added.