What do you like best?
I personally value the integration a lot. Often enough you run into amazing hardware, or software, only to then find that other parts are missing. With Particle, the road from 'prototype to production' is made a lot easier and more accessible since they offer all aspects required for it; Dev tools, hardware, software, cloud, everything you need to get your product or project connected and talking to the internet. Seeing as (almost) everything is open-sourced, you're not forced into all of their tools, in case you'd like to use something else, but they're there if you need them.
Furthermore, their human side is very important to me. Particle values its customers, and more specifically, their maker community. Having been there since the early days, I can't stress enough how valuable it is to have some of the people behind the products engaging with the customers directly (the community forums for example). Feedback is taken from the community and taken into consideration when developing the platform further, which is a very nice feat to encounter.
What do you dislike?
Not much. The tools, hardware, software, and community support is a package deal unlikely to be found elsewhere. Sure there, might be some minor UI 'issues' that I can get finicky about if I looked for them, but they're negligible in the grand scheme of what the platform as a whole has to offer. There certainly aren't any deal-breakers as far as I'm concerned.
Recommendations to others considering the product:
I can't recommend Particle enough. The experiences I've had with their products, as well as with the people behind it, were and still are truly delightful. The combination of very skilled professionals who create amazing product while actually caring about what the customer thinks of them is immensely valuable in my opinion. Using the platform has definitely been of added value to me, as I'm positive it can be for others. Pricing is fair enough that nothing is lost by giving them a chance, which I'm sure few will regret.
What problems are you solving with the product? What benefits have you realized?
Using the Particle platform allows one to go from a single prototype, back-of-the-napkin style idea, to a well thought out product in a time frame that wasn't realistic up until now. The same module you're using for prototyping can also be deployed inside a finished product as many others have already done. When looking at scaling, there are options available too that allow one to go into mass production, using the same platform you're familiar with from the smaller scale, thus saving a lot of time and money.