@Abcd3 The instructions on mine say to use every 2 weeks for 8 weeks. Then you only need to maintain by using once every 3-4 months.
It is completely unnecessary and pointless to use it more often than every two weeks in the initial phase btw, as any growth during that time is due to follicles which were naturally in a resting phase becoming active.
In practice my leg and armpit hair vanished after only 6 weeks and I only used it a 4th time on my beard and 'tache, about a month afterwards. I used it once or twice at 4 month intervals over the Summer/Autumn after that, and let it lapse over the Winter. I still have almost no armpit hair at all, and my leg hairs are far sparser.
@Oddgirlout It is not permanent. It causes hair follicles to go into a resting phase and stops growth that way. The Tria works in exactly the same way despite its very cleverly written (dishonest actually) marketing material - neither destroy the hair follicles and so neither are permanent. Regrowth with both will eventually happen if you stop topping up occasionally. However as many have posted, including me, regrowth can be sparse.
Like many other posters I found the extra attachments for various parts of the body completely unnecessary and I don't use them or need to use them. Phillips often price their personal health products (epilators, toothbrushes etc) in increments with incremental extra features and in my absolute experience you don't need or won't use almost all of them! Base model will be therefor best and cheapest. So no, you don't need an extra window for face hairs or whatever they think up to upsell to you (use the strength settings instead for sensitive areas), and you definitely don't need cordless.
You DO need as big a window as possible or it will take ages to use on a large area such as a leg, and the very cheapest Lumea model which is a completely different shape is really too small for large areas. All the others are almost identical.