Pros
Having flitted around the PR landscape for many years prior to joining ABI, I've seen all manner of agencies - both big and small. What has always stood out in my impression of ABI is its incredible corporate culture. Every single one of my many colleagues over the years have been fantastic to work - and drink! - with. As a smaller agency, working for clients who initially don't see the immediate value of marketing, it is essential to have a cool, fun and smart team who support one another at all times. ABI takes great pains to only hire people who will be a good fit for the agency culture, and it shows in the many friends and connections we all have, even after they have moved on from the company. personally, I have found the work to be both challenging and interesting - although the intricacies of B2B marketing may not be for everyone. You need be detail-oriented and to thrive on speed learning some quite obscure technologies. But if you persevere, you'll succeed in a firm that wants to give you as much responsibility as you can handle. Though I've since moved on, I would recommend ABI as a unique place to work.
Cons
I would say the cons are less to do with the agency and more to do with the clients - not all of the businesses you might work in are necessarily that engaging. The client personalities can also be quite challenging to work with. That said, if you can handle them, then you've learned a very marketable skill in it's own right. I think ABI struggles at times - as all smaller niche firms do - with finding and retaining staff. But during my time there we had several colleagues who had stayed with the agency for over 10 years, while others had come back after leaving, so they're doing something right. You're not going to get rich doing a PR job, these days, but at least here you'll learn a lot.