Wow I found otherwise. EX1 by itself was more work than Eng Adv in year 11 from my experience. 4 unit maths is vastly different from 2 unit lol.
Truth.
And 4U English is a whole different kettle of fish from 3 or 2U English.
If we're talking EFFORT NEEDED + SCALING --> BENEFITS, then if one was
good at and liked Maths, I'd say 3U and 4U Maths are definitely worth it.
Slightly less "worth it" in terms of humanities extensions (ie. 3/4U English, or History Extension) because EFFORT needed is relatively more, and SCALING effect is relatively less. But if one is good at and liked it, then it would still be worth it.
Any of the extensions are "not worth it" when one
isn't good at or
don't like the subjects particularly. In that case its probably wise to just stick to a level that's comfortable.
ETA: I forgot the languages. I'd say that most language extensions are definitely worth it. In the case of Latin or Greek, its simply more of the same - hence not too much extra effort required and great scaling. For other languages, ie French/German/Japanese the focus is more on culture, but it is extremely helpful in increasing your fluency in the language and will probably boost your 2U studies.