It sounds like the group is funded towards a certain goal
I wouldn't be put off, it just means that it will be very focused - this can be good or bad - sometimes they can be quite high pressure - deadlines expected - but with an organsied supervisor this should not be too bad - but essentially your project would be doing work to fit in with what they want
It depends what YOUR goal is?
A- any old PhD as long as its a good one that'll get you published - this one sounds fine
B - you have some rough ideas of the field you want, you'd prefer to develop your ideas in conjunction with the supervisor, but ultimately you want to decide the direction - this might not be for you
I would still go talk to them and find out the limits though -you never know it might not be that bad