1. Your experience at Meltwater will depend heavily on who your manager is, and how experienced he/she is at managing others. If you end up with a manager who is less experienced, be prepared to be micromanaged. I found that managers who have been there for a shorter amount of time tend to be more centered on achieving their personal sales goals, as opposed to helping achieving their team/office goals.
2. Expect to have very little work/life balance. Unless you are hitting quota, there is not much appreciation put into the work you are doing. You will work the minimum 8 hours per day in the office down to the minute, and be expected to work multiple hours per day outside of the office.
3. You might not be totally comfortable with the way you are told to sell something, or how you end up closing a deal. There is a certain pushiness to the sales tactics that might make you feel like you are not doing the moral thing, this of course is dependent upon the type of person you are.
4. I wouldn't go as far as saying that the atmosphere is "cult-like" but there is a definite persuasion to love, live and breathe everything that is Meltwater.
Overall, if you want to learn the sales process and have no previous sales training, this is a great company to spend a few months at, but don't count on it being long-term, as you'll most likely be burnt out before you can succeed.