RAI (or snorkel to the uninitiated) was invented in Australia for that particular reason.
>>> do RAI really keep the air filter clean ?
Yes, for longer...
>>> Are they worth the monetary effort ?
They don't cost an arm and a leg ...
>>> Or cleaning manually the filter after the more dusty sections is good enough (as I have been doing for a while..) ?
I'd rather have a cool
>>> Should I expect a significant loss of power in the engine ?
Not likely, if properly installed ...