This is a pre-assembled Luxman vacuum tube harmonizer kit, the LXV-OT6 mkII, released by ONTOMO SHOP. Its main feature is the ability to vary the harmonizing effect. I think it's particularly good that it doesn't use an AC adapter and applies 100V to the B power supply, so there's no switching noise. You can feel the effect when combined with a digital amplifier. Insulators are attached to the feet with double-sided tape. The original rubber feet are also included, so you can use whichever you prefer. I'm selling it because I switched to a main vacuum tube amplifier and haven't used it much.