As noted in a previous post, the "i" version has a microphone while the other doesn't. However, something worth noting is that it
only works with iPhone, so if you have an Android phone much of the in-line control functionality won't work without an adapter.
On the topic of recommendations, I would definitely go for the MA750s (your pick if whether or not to get a mic, I'd personally skip it to save a little cash since I use a smartwatch and don't need in-line controls and don't care enough for a mic, but that's me, you're your own case). They sound amazing for their price. Bass is moderately loud, nice and punchy, but not overbearing and doesn't bleed into or cloud the mids or highs. Mids are crisp and clear, though ever so slightly recessed. Highs are creamy and forward a bit (though slightly sibilant on occasion, but that usually happens due to how the track is mastered). Overall they have a sort of more well rounded v-shape sound. They work wonders for rock, pop, EDM, jazz, R&B; throw basically anything at them and they sound amazing (they're some of the most versatile IEMs I have ever used).
Additionally, they handle EQ very well, so feel free to alter the sound slightly with EQ if you don't like them right away. Something also worth keeping in mind is that the MA750s have a pretty significant burn-in time (from my experience). While they sounded great out if the box (to me) they didn't sound their
best until nearly a month later (a month of normal use, not consecutive playback time. I'd estimate the consecutive runtime necessary for burn-in at around 60-75 hours total).
Another thing to keep in mind is that they aren't the most comfortable out of the box; the included silicone tips suck and the over-ear style can take a little getting used to. IMO though long term the over-ear style is
much more comfortable when you get used to it and decreases microphonics (the sound you hear that the cable makes when it's moving around or hits something) to near non-existent. On the topic of eartips though; get comply tips (I used the new comply sport tips on mine. I believe they actually come with a pair of comply comfort tips nowadays), they improve fit, comfort, isolation, and overall sound quality immensely and are definitely worth the recurring $20 every few months.
Another good thing to know is that RHA's support is amazing; if anything happens to your pair and it's still covered under warranty then RHA will be almost guaranteed to have a solution, going so far as to just send a new pair at no cost if something is damaged (depending on what it is).
Overall, though, the RHA MA750s are amazing. I personally just upgraded away from them and didn't find a significant increase in quality until I started spending over $300, more than twice the cost if a pair of MA750s. IMO the MA750s outperform every other IEM in their class and even outperform many IEMs above them.
Also, sorry if I sound like I'm fanboying (tbh I kinda am). I really do believe this is an amazing option though, so that's my two cents on the topic.
