I've been to Udupi many times, in groups, pairs, and on my own. I've learned that it's best to just get the buffet, particularly if you like your food spicy, because no matter how spicy you tell the waiters you want it, they'll give you no spice at all. The buffet, however, has nice, spicy, authentic, vegetarian Indian food. Lots of options for vegans as well. If you do get the buffet, the waiters will also bring delicious, crispy, potato-filled Dosas to the table, as many as you want, at no extra charge.
Cons: Menu ordering not great