I bought a pair of Monster iSport last week.
This is not my first IEM. I already had Etymotic ER-6 (hate them !, They were too big for my ears. They never fitted, and they stopped working completely for no reason !), and JVC HA-FXC50 (love them).
Unfortunately my FXC50 got quite used, I have them for three years and they don't sound good any more. I love the wing which fit the device in the ear very nicely. They were very confortable, and I can put them in my ear in one second. They also provide rather good isolation.
The iSport has another shape. They are not as easy to put on (it takes me 10 seconds to wear them).
They don't provide as much isolation. (slightly less)
ljokerl rated the HA-FXC50 in http://www.head-fi.org/t/478568/multi-iem-review-238-iems-compared-astrotec-am-90-added-05-21-12
as Confort: 3 / 5 and Isolation: 3.5 / 5 (it seems I would have rated them Confort: 4.5 / 5, but I'll stick to ljokerl rating for comparaison)
Using the same scale I would rate the iSport as Confort: 2 / 5 and Isolation 3 / 5.
They came with 5 ear clips and 5 ear tips (XS, S, N, L, XL). I choose the S ear tips and the N ear tips. They fit pretty well, but my left ear hurts after 1 hour. Maybe I will get used to it. My right ear doesn't have any problem (rate confort: 2.5)
Now for the sound. I cannot compare to my JVC FXC50, because they no longer sound good, but I am very, VERY, satisfied with the sound of the iSport. See the attached screenshot of Foobar equalizer. The correction is so light that I am very pleased to the sound without correction (in my mp3 player, while running, or working).
The frequency response is pretty flat, including the low end. They also go lower (20 Hz). The bass are really awesome, medium is good also, and the treble are pleasantly clear without being harsh.
So I am very pleased by my purchase. I will also receive a pair of JVC HA-FXC80 in one week. I will update my post some time after.