Pros
I worked at Castleford for one year, predominantly in 2014 and had some great colleagues. It was my first 'real' job once I finished university. You absolutely need to knuckle down to meet client demands and produce enough content, however during my time at this company I made some fantastic friends and developed skills that proved transferable not only to my next job, but another industry entirely. Such skills include meeting deadlines, being able to switch from one task to another without losing momentum, time management, and writing engaging, persuasive content. There's also room to develop client relationship skills, however I was working in the editorial team as a writer, so the bulk of client management fell on the account managers (based in Sydney). The people are great. You will need to be incredibly diligent with your time - it's a precious commodity as a writer! As a graduate job, it set me up well for my next role in a different industry (albeit one that has a strong focus on the written word!). It's really what you make of it. For me it wasn't a long-term role, and it wasn't the easiest job at times, but it set me up well for my next job and I'm still great friends with some of the people I worked alongside.
Cons
You have daily, weekly and monthly targets for content production. So there can be a detrimental flow-on effect if you write slightly less one day and/or one week. I guess this is applicable in any job, but because from an editorial perspective your workload is so compartmentalised (i.e. by client, and within that by the number of articles of a particular word length every week/month) rather than being project-based/results based, the sheer quantity and sense of "meeting target" can be overwhelming. Again, this is what you make of it. My view would be to perform well in the entry-level roles and shift into something like the senior content writer role, which requires less content production given you've got a more hands-on role with clients.