I have used vegetarian suet for years in Christmas pud and mince pies and I defy anyone to taste the difference. The fat in these items is to keep them moist, not to add flavour to dishes stuffed full of fruit, spice, booze & sugar; you simply can't taste it.
Fish & chips are best fried in beef fat because you CAN taste the difference. Pastry is best made (IMHO) with a mixture of butter and lard, for optimum flavour & crispness. Potatoes roasted in lard are the crispest by far, no matter what chefs may tell you about duck or goose fat.