I was very close to going with Hillcrest. They have beautiful windows. However, I don't blame you for being edgy.
I eventually settled with a company in Omagh. They insisted on 50% upfront and the remainder on delivery (before the windows were taken off the truck!).
I got them installed and they are beautiful and great quality. Obviously there are some small snags. However, they have recently gone into liquidation so bang goes my snag list and my 10-year guarantee. It could be worse though.
They were a great company and far from gangsters (I am led to believe that a recent family bereavement significantly contributed to their closure).
Best of Luck either way