I just finished a game on deity with a pangea map as Portugal the other day, and I found I really enjoyed the Feitorias and that they were a big help mid game. Luckily about 5 of the 8-9 city states in my vicinity were coastal and I could use them. The Nau I didn't get to use that game, sadly, since my empire was mostly based around an inland sea with only a couple of my cities and 1 city state on it, but it's been decently useful in other games for me.
I got a pretty good tech pace going and a couple of my cities were eligible for observatories, so since I got observatories already, I just went for Navigation to get Feitorias after too. I agree it can be a detour, especially when it's a pangea map like I played, but it felt worth it seeing as I wasn't far off from it anyway.
I ended up winning a diplo victory since I couldn't be bothered to slug through Shaka's sprawling empire north of me to reach his capital. But before I was able to consistently secure the city states late game, I liked the Fetorias giving me lots of happiness from the ones I couldn't afford to out-pay the AI on in the mid game. It let me relax on making some happiness buildings to focus on other things I wanted to keep going.
I'd say the Dutch are more consistent since they only really hope to have Polder-able lands and their UA is usable any point in the game. Portugal really wants coastal access for Naus and coastal city states to put Fetorias on, and then both only come up mid-game. Their UA is ok but it doesn't feel like much extra gold to me. However, I still think I like Portugal better even if it's just Fetorias I really get to make use of. Not saying they're stronger, just they're less boring than the Dutch to me. Something's really satisfying about dropping a Fetoria at a city state allied with somebody else, and Nau's can be neat when you get a chance.