umbrella

Looking to buy a shoot through umbrella. I have 2 options. Pay £15,000 or £30? I am by no means a beginner, but also not a pro studio. I plan to use the umbrella for real estate in certain situations as well as portrait stuff. What should I really be looking for?

Any useful comments or experience on using the shallower parabolic umbrellas? I thought I might have a play with one and am wondering how others put them to use?