Does anyone here have experience with the Linhof shoe-mounted gadget that optically and mechanically shows the view seen by different focal lengths? Is it worth the effort to carry it around as opposed to my trusty card with a 4:5 hole cut in it? The ones I have seen on ebay seem to have a maximum focal length of 360 mm; are some longer? Are they still sold new? Does anyone know of alternative (i.e. lighter or cheaper) gadgets other than a simple card? <p> Thanks.