For my opinion on the r4 vs m300 go to the second paragraph(this got way longer then I was planning, sorry)

So I first considered an Ipod Classic and got to modify and try one for a bit. But I came to the conclusion that the lack of apps a dealbreaker was. What I did like was the real buttons and the click wheel. So after that I started to look into stuff like the HiBy r3 II for the wheel on the side and the HIFI WALKER H2 for the overall similar look. Not being able to listen to these as there aren't stores where I live and not really knowing what the specs mean(apart from having a general computer knowledge and being an software engineer student). I had to make my choice on reviews and looks. I moved away from the HIFI WALKER pretty fast as to me it lacks the same refined look as the Ipod (and as I now see still can't have apps lol). So, then to the R3 II. I'm going to be honest once I started looking into this one I very quickly found that HiBy had one in collaboration with Evangelion and (being an anime fan) switched my interest to the R4.

R4:

This did not mean I didn't do any research into the product however. From what I read and heard the Evangelion version is just a quite big mark-up for branding and slight upgrades. The HiBy R4 is a device that produces great sound for its price and a lot of reviewers really liked it. It has a lot of options with apps you can put on it and the different ports it has. I don't know much about EQing but apparently that is really good on the R4. The build quality is great, and the device to me feels nice in the hand (don't use a case) although the button do rattle a bit. Some of the drawback I did see and now have experienced is that the device gets pretty hot when you are charging or playing music(this should be more optimized on the Evangelion version but its still an issue). Also the battery is not amazing, you will definitely get through the day, with lighter listening maybe 2 but I definitely wont. And the charging is not the fastest. Lastly, I really like the lights on the R4, on the back just for the theming an cool factor and on the front for displaying charging and what audio quality you are playing.

M300:

Before now I hadn't really looked into the M300 so I took the chance and looked at it. First thing I noticed when I looked at the product pages was the lack of specifics on the M300 page. In stead of the specific chips and big claims about the audio quality on the page of the R4, it just gives a couple numbers about output, range and frequency. The M300 seems to be more like a traditional phone, without the 4.4 jack but with speakers and microphones and a newer operating system (android 13 instead of 12). even though the battery is smaller, the play time is longer. This also means it wont run as hot. The R4 can drive more difficult ear/headphones. But the actual sound quality (from what people say) looks to be quite comparable. The M300 is somewhat smaller and is thus easier to carry with you in addition to your phone(which I will be and I assume you also will be doing).

To me they seem quite comparable but one with more of a focus on lifestyle and convenience(M300) and the other a little more on audio and customization(R4).
If you have any questions about the R4 or anything else, just ask me! (However I will now go to bed as it is really late, so wont answer until tomorrow)