Its a good company but i would think about the loss of perks and benefits if you go from perm to contract and also the real fact that you could be contract for 3/4 years in the role - do you need to get a mortgage in that time - it may pose a problem as bankers are tightening their lending restrictions etc right now, are you planning on having children etc which could impact your decision
If its an area where you want to get into then i reckon go for it, sitting in a perm job just for security is not a good enought excuse in my opinion.
After pfizer going down there, there is no security in even permanenet jobs so if you feel its right for you go for it.