Putting the finishing touches to my new studio setup I discovered that my plan to use my laptop on top of my 19" rack was a problem, and this sliding rack shelf solved that problem right away. I carefully measured the height of my laptop to ensure that, when closed, it would slide into a 1U space without problems, and bought this unit almost immediately.
Fitting it can be tricky, since it has rack ears at the front and back of the unit that need to be adjusted to fit. My rack is deep and I needed to remove the rear ears and refit them to a further set of bolt-fittings on the sliding section for extra depth. There are two Philips-head bolts each side to adjust, and sometimes they can be hidden behind the sliding section which needs to be moved to a suitable position for them to be loosened and tightened. The reach required is easy to assess, although it is easier in an empty rack. Mine is full and it was easy enough to measure the necessary distance between the front and rear pairs of rack ears. Getting the fully-adjusted shelf into a full rack is also tricky, the runners are barely flexible enough to allow free passage through the inside of the rack. This unit is better fitted into an empty rack since it can be tilted sideways and then leveled out to be attached front and back.
In use it is excellent, free moving and very stable for my laptop.
The available shelf size (about 42Wx33Dcm) is fine for laptops to be used and stored, but 17" and probably also 15" laptops will need to be used from either side of the drawer rather than facing the rack since they are a tight fit onto the shelf unless they are put in sideways (remember that connectors also tend to go into ports on each side rather than at the rear of a laptop, so space needs to be allowed for cabling). My laptop is 3.33cm high and can be stored inside the rack without any problems. Cables to interfaces etc can be fed out of the back of the unit, but only small interfaces could be kept on the shelf along with a laptop (perhaps the Emu 2x2).
Of course the unit could be used for other purposes, allowing smaller non-rack effects units to be racked, used to store cables or even interface units that are nicer hidden from sight. If, unlike me, you can use your laptop on top of your rack, the shelf can still hide all the PC-related clutter to give you a sleek work surface!