All of my bikes, including my Brompton, are on BikeRegister. For all but one I used the stencil and marking compound kit. My carbon Quest has neither paint nor powdercoat and so has the QR code tamperproof stickers, one obvious and one hidden. You get one sticker with the stencil kit, and two if you're doing QR codes.
I'm also a cycle champion at my work, and I've security marked probably two hundred bikes with BikeRegister. The 'virtually invisible' method, which I presume is the marking compound, results in small navy blue dots that fluoresce under UV light. The end result ranges from visible but unobtrusive on white paint, to very unobtrusive on dark grey or black paint, to completely invisible for all practical purposes on matt metallic paints. Not everyone at my work has opted to have the marking compound, but most have. And almost everyone has put the tamperproof sticker(s) on their bike; some prefer the top tube, some prefer the down tube, some underneath the downtube; and those with Bromptons tend to have the sticker on the main frame ahead of the front hinge, and the stencil on the seat tube.