Posting a (non-original research) Masters thesis on arXiv? Based on the following posts:
Posting master&#39;s thesis on arxiv?
Should one put their Master&#39;s thesis online?
although my question differs in that my &quot;Master's thesis&quot; was not part of a formal Masters program. Rather it is more of an extensive reading project that I did over the last 10 months under a very well-known advisor in my field through the Fulbright Scholarship. I've a 150+ page review on a topic I think would be of interested to others in my field at my level of knowledge. However it does not contain anything new, and I think this means it has no place on the arXiv. It solely summarizes the inception of a topic from the 1960s, and summarizes a new take on the topic that my adviser uncovered in some seminal work around 2010.
Can I get some input on the pros and cons of posting it on the arxiv/ inspireHEP profile?
Pros:

easy to send to friends, peers, potential collaborators, and most importantly, potential PhD advisors at my uni

Cons:

it might look petty/immature
In my field (cosmology), plenty of researchers and professors post lecture notes on arXiv, and of course many people write and publish review articles which don't contain any new results. So there's no requirement of novelty to post on arXiv.
Whether it looks immature largely depends on the quality of your writing. A poorly written review will not be read, and could reflect badly on you if you continue in academia (employers and grant reviewers will look at your Inspire and/or ADS profile). Bear in mind that you can't remove things from arXiv.
I would highly recommend asking your supervisor about this. They are best placed to tell you whether it's appropriate or not, according to the quality of your work and the conventions in your field. If you don't post on arXiv, you could consider uploading the pdf to your own website, a public github repository, google drive or similar. Then you can still share the link with interested people.