As with so many of the questions asked of this group, there are so many variables that go into determining the "right" decision.
In this case, what are your marketing objectives and how will PR help you achieve those? What are your expectations for PR? What are the realistic opportunities for media coverage in your space for your company? How important are personal relationships with press/bloggers/influencers? What's your budget? What are your internal resources capable of handling? What strategies do you think will get you results e.g. spray and pray, relationships, etc. Are there PR contractors who might have what you need or internal people at a much lower cost and better ROI? And more.
But to your question about personal experience, I'll share one example:
I joined a startup that was paying $10k a month for a very good PR firm. The company had a CMO (who I replaced) who was enamored with the idea of having a reputable PR firm. Problem - the firm was not delivering $10k/month in value. They had secured very little media coverage and not much value in other areas. I discovered they did not have relationships in the space and were not having much luck establishing relationships. And worse, as I looked at the space (new one to me) the reality was there was not a huge upside in potential coverage based on our product and the market trends. And they really didn't deeply understand our company.
So two weeks after I started I put the firm on notice and terminated the agreement. (They were great and agreed with me.) I then did the PR myself, reaching out to the media and influencers in the space. My emails coming from the company seemed to have much greater success in getting a response and building relationships than the PR firm. And the relationships benefited our company in many ways besides just media coverage (especially around content marketing). Did get some press coverage that was beneficial although not a huge amount. And importantly I personally learned so much about the space by doing it myself, things that helped me in every other aspect of marketing I did.
But I was at another startup that used an agency and through their relationships got us on the Today Show and some other great coverage that wouldn't have happened otherwise. It was an important part of the initial growth.
So back to my original point that it's all about your specific circumstances.
Best of luck.