There is no cashew feni worth drinking that is marketed commercially. To get the real elixir of Goa, its state drink, its primary tipple, you need to get someone who knows an old lady who still distills the stuff in her backyard.
When the Portuguese came to India, looking for souls and spices, they brought with them tomatoes, potatoes, chillies, chikoos, papayas, pineapples and cashews. Every one eats the nuts; Goans eat the fruit that hangs above the nut too. But eating it, most secretly believe, is a waste. Because every fruit that is eaten means less that goes into the still. The juicy red and yellow fruit ripens between February and May. The ripe cashew fruit after being separated from the seeds (cashew nuts) are crushed under the feet in a special rock-cut basin. The juice is then fermented in barrels for a few days and distilled in earthen pots. The resulting brew, called modap, is mixed with more fermented juice and distilled a second time to get a drink called cashew uhrak, which is much lighter than cashew feni.
Uhrak is mixed with a mixture of an aerated lime drink and soda, with a pinch of salt and a twist of lime. When uhrak is mixed with more fermented juice and redistilled, you get feni.