I have all three. What would you like to know specifically?
In general, the H40 is very full sounding and is very efficient. It gets loud at low volume levels. It has a very natural sound stage but the H40 is a relaxed tuning. It is not very detailed but is fun. The H40 has a long extension into your ear and can cause suction issues with certain tips. I spend a lot of my listening time with the Mangird Tea and the H40 adjusting them to relieve inner ear pressure. The Fiio IEMs are a MUCH better fit for me and have no inner ear suction problems. The Fiio has a similar tuning to the H40 but with better imaging and detail.
The Starfield is harder to drive than the H40 or FH3. The Starfield sounds more clinical than either the H40 or FH3. I personally feel the Starfield, although being a very good value at its price point sounds thin to heavier hitting IEMs.
Of all the IEMs I own, the FH3 has become my favorite mainly for overall sound enjoyment, slam and comfort. They have left me feeling quite fulfilled and uninterested in continuing the search for the perfect IEM. At 130 bucks, the FH3 is just 20 dollars more than the Starfield and is much less expensive than the H40.
