I still think RE300 is an excellent pair of IEM earbuds. I continue referring to them as my headphone ear-plugs because their noise isolation with a right set of eartips is really at the top of its game. They go deep into your ear, disappear like earplugs, and seal it well to deliver a very clear sound with a nice enhanced bass. These are not audiophile quality IEMs with a fatigue high frequencies or basshead IEMs with a booming veiled bass that makes everything else disappear. They are just great for everyday use, especially when you need a great sound isolation and don't want anything to stick out of your ear too much
But something was bothering me since I only got a chance to test/review RE300H, their audiophile version, while I read some comments saying A-android and I-apple versions differ in sound with a more booming and distracting bass. Finally, I got a chance to get my hands on a review sample of RE300A Android version of these IEMs which you can still get for under $50 from Penonaudio: http://penonaudio.com/HIFIMAN-RE300A . Penon actually recognized the value of isolation these earbuds provide, and now they are offering a bonus of 3 pairs of eartips, two double-flange and one triple-flange versions. Unfortunately, my earcanal is not deep enough to test multi-flange eartips, so I typically use single flange ones. I can only imagine how much better isolation is going to be with these tips.
The design and packaging of these is IDENTICAL, with an exception that my 300H was US version while 300A is Chinese versions, and it's reflected in the text on the box. But it really doesn't matter, these are headphones - no need for instructions

Even the in-line remote, it's universal for any phone and should be self explanatory. I think it could work not only with android but also with apple since I never had issues with Apple remotes on my Galaxy phones. That is the only main difference, an included in-line remote with a single multi-function button that works perfectly for Play/Pause/Call with a single click, Skip Next with a double click, Skip Back with a triple click, and start Google search with a long press.
Another difference is the cable where RE300H has a more rubbery/sticky finish versus RE300A having a more plasticky smoother finish. But that's just a finish. Inside of the cable, RE300H uses different wires for a higher quality sound while RE300A has an advantage of in-line remote to pickup calls and to control the music. I think both models compliment each other well. Just think about it, when you are outside or commuting, with RE300x in your ears you can easily miss the call, so inline remote has an advantage. But when you are at home relaxing and want to tune out screaming of your kids (speaking from a personal experience), RE300H will work equally great.
Regarding sound itself, I do NOT hear any mid-bass bloat from either RE300A or RE300H. H might have a little more sparkle in the sound and according to the spec should have a slightly better extension at the low/high ends, but A sounds very similar. I had 300A on burn in for almost 60 hrs, and it sounds very clear and balanced and still has an excellent bass slam which doesn't overshadows the rest of the frequency range.
So for those who are still deciding between which one to get, based on my testing and comparison - they are VERY similar in sound signature and quality. Just keep in mind if you want a little more sparkle and slightly better retrieval of details, go for H. But if you want a convenience of smartphone control - A is great for that! And if you are lucky enough to be able to use double-/triple-flange tips - Penon got your covered with a free set of bonus eartips, not to forget their shipment is always super fast.
Here are the pictures (click to enlarge).
Bonus eartips.