I am really enjoying it as it turns out. It is time-consuming - each round of 400 plus stitches is taking me about 45 minutes at the moment - but the pattern itself is a lot easier than the bigger motifs in fair isle knitting and can be memorised fairly quickly , so that after the first repeat or two, I don't keep having to check the chart and can get on with watching Lewis or King or whatever.
The Luckenbooth brooch is a traditional Scottish, rather than Shetlandic/Norse, symbol. They are named after the Lucken Booths, or 'locked booths' - early shops around St. Giles Cathedral in Edinburgh, that sold jewellery and trinkets. The broochy were often given as a betrothal gift, and later pinned to the shawls of babies to protect them from evil spirits. Normally made of silver, a Luckenbooth brooch consists of two intertwined hearts, often topped with a crown. Lots of modern examples on Etsy