personally I have a range of heads from Paul C Buff. unfortunately not the Einstein 640 so I can not comment on that head specifically, however I can say good things about my alien bees. which are of lower quality. I have the beauty dish and have gotten some good results with it. I will say that I found there to be trade offs with the alien bees when I compare them to other mono-lights I have used or even my canon flashes.
However as I am not a professional, just a serious hobbyist, so if I lack certain things it bothers me much less.
for me i wouldn't go back and do it any differently.
I have 2 b400, 2b800, and the ring flash (arb800) with a whole slew of light modifiers. If i wanted to have a the same flexibility of options with a profoto or elinchrom for example, I am sure I would have to spend 2-4 times as much.
I haven't really directly answered your question, but this is my advise. If you are trying/actually making money with your photography, that is as your primary income I would go with the best system you can, profoto in my region is the industry standard. I know a few young photographers and they are all using elinchrom or profoto. as such finding readily available rentals, light mods is easy. so by starting with a high end system and slowly adding to it you will be less worried if it breaks as you can rent if needed. But if you just enjoy photography and occasionally make money then the Einstein will make you very happy and any delays in purchasing light mods and more lights is really a non issue as it wont really "cost" you downtime.
Note I think this way primary because of the availability and consistency of the lights rather then the final image result. As in the hands of a truly amazing photographer I believe he/she, in most cases could produce amazing images from either system.
