What are the pros and cons of getting an MBA when you're already in product marketing/marketing and looking to stay in this field and under what circumstances does an MBA help?

Most of my career has been spent in Marketing and I used my MBA to transition industries (from CPG to Tech) and location (from Latin America/regional teams to the United States/global teams). 

While I had practical experience as a Marketer, what I learned through my MBA is the strategic and analytical side of marketing - focusing on understanding what frameworks are best to solve different problems, what data and insights I need to inform my decisioning process, and how to measure success of different aspects of the business. During the early stage of my career, the Marketing work I did was very executional - heavy on launching products/brands, running campaigns, etc. An MBA allowed me to level-up and understand why these actions were needed and how they impacted the broader business, and in the case of Tech, the overall portfolio of products.

Personally, I think an MBA allows you to focus on strategy, understand how your peers have tackled problems in different roles/industries, and how Marketing fits into the bigger picture. Even if you've done Product Marketing before I think there's real value in pursuing it, in particular if your previous experience is in startups and/or more executional roles at bigger companies, which tends to be what folks focus on in the early years of their professional life.

MBA certainly provides access to a network and usually a world-class quality education and introduction to marketing frameworks which are useful in any marketing job. But it also comes with a huge opportunity, and often, financial cost

My personal take is that MBA can help in functional transitions but may not be required if you are already in marketing/ product marketing. I am a fan of learning on the job which MBA cannot provide

It really depends on your goals and the current situation. In my humble opinion, the value of an MBA is likely to be higher if one or a few of the following things are true about you:
1. You're trying to change your role/function (and having a hard time doing it without a degree)
2. You're trying to change the industry (and having a hard time doing it without a degree)
3. You're trying to change the geo, e.g. move to the US or to the EU (and having a hard time doing it without a degree)
4. Your undergrad major wasn't business or econ
5. You want to learn more about other business functions, such as Finance, Strategy, and Operations

Based on what you described, it's unlikely (but possible) that an MBA degree is going to be tremendously helpful to you as you're not planning to change anything.

Disclaimer: I earned an MBA from Berkeley-Haas and found it useful in many ways. That being said, many things from the list above applied to me. Overall, having an MBA is definitely not critical or necessary for a successful career – there are many paths one can take to achieve the same goals.

Perhaps this is controversial, but I would say there are zero pros and many, many cons.

MBAs can be useful if you're looking to switch fields. Otherwise, I'd much rather see two additional years of work experience. I've hired MBAs from top 15 schools and from a PMM perspective, I was basically starting from the same place as someone without a degree. 

If you are literally looking to stay in product marketing or marketing (and already have a job in the field) then I would agree with the other posters that an MBA is not going to get you much.

However, if you have designs to move into (strategic) product management, start your own company, or something else adjacent to where you currently are, then an MBA can be useful, particularly if you don't have an undergraduate business degree. That said, if you plan to move into product, I would actually say that the ability to work with a delivery team (e.g. engineering) and having the domain expertise / empathy for their world is more important.

MBAs are definitely great if you are switching fields. They are also great from a networking perspective.  

There are plenty of people who studied business or marketing as an undergrad who have gone on to have successful PMM careers.

The MBA is a classic example of selection bias. The type of person likely to get an MBA tends to be more motivated and talented than average. Thus if you take a pool of MBAs vs. non-MBAs with equal experience you will get a more successful group from the MBA pool. This does not mean the MBA curriculum made them better, but it is a useful shortcut when recruiting. Hiring managers frequently lean on this. Obviously there are many exceptions to this generality.