This is a common deal in this industry, and the terms are fairly standardized. They get a small stake, and usually something like follow-on rights, sometimes more. In this case, Pfizer invested further after that. The big drug companies have a very large stake in making sure departing employees aren't scared of taking this particular deal because they write off a ton of drugs this way, and the only way to profitability on that IP is if someone takes the IP and takes the vast majority of the risk and cost, as this guy has. Don't think I've ever heard of an instance where someone took this deal and got screwed by doing so -- only instances where someone didn't (or tried to weasel out of the deal) and then ended up screwed.
