There are pros and cons to anything, and being an in-house translator is no exception. I went pretty much from studying to working in-house; after finishing a translation degree I completed a translation traineeship at the European Parliament, and shortly thereafter I was hired as an in-house translator by a relatively small agency based in Scotland. I worked there for almost two and a half years, and very recently - at the start of the year - I became a freelancer.
I think starting out in-house is extremely helpful. You gain valuable experience, you build up your confidence, you observe the translation world and how it all works. I learnt so much during my time there and when I started I was convinced I would never go freelance. I was lucky enough to have wonderful colleagues, the projects were varied and interesting most of the time, I finished at 5pm and could forget about work, all evenings and weekends were mine.
After two and a half years, however, the downsides started to become harder and harder to ignore. My salary left much to be desired; given how popular my language combinations were, I pretty much worked non-stop and my workload often covered more than double my salary, based purely on the word count and what freelancers were paid (which wasn't very much). My commute lasted between an hour and an hour and a half one way, not to mention the monthly train pass cost an absolute fortune. I fought for a raise for a year and a half and finally gave up.
I've now been a freelancer for only two weeks so my feelings might change, but so far I'm absolutely loving it. I have three hours more in my day and I make my former daily wage in the time it used to take me to commute. I decide what projects I want or don't want. I can work from anywhere and go see my family whenever I want (currently working from my parents' living room in Brussels). I have more time to read, cook, exercise, do anything I want. I can pop out to the dentist or GP or shop if necessary. My cat is over the moon. The only real downside is that I miss my lovely colleagues, but I just make sure I see friends and family often.
I don't think I could ever go back unless I was given an extremely attractive offer, and considering how stingy agencies are, I think a good enough offer could only come from an international organisation like NATO or the EU. I think going from in-house to freelance is great, but freelance to in-house would be very difficult in my opinion. Much also depends on your language combinations, of course. If you were offered a great salary and worked for a friendly company, the stability of a permanent job could be quite tempting, though I think I would hate having someone dictate my holidays again. A good point made in the article you mention is that as an established freelancer switching to an in-house position, you would have to give up some clients, and even after only two weeks I have some that I wouldn't want to give up. In short, I'm much happier and better off financially. We'll see how I feel further down the road! Good luck with whatever you decide - an irresistible offer could may well come your way, you never know!