Hi Igorian
Window companies are a nightmare. I remember when I had quotes a couple of years ago and one salesman really put the pressure on for me to sign that night, he stayed til about 10pm. I suppose he thought he could pressure me into it because i was living on my own at the time. Other companies rang me every few weeks to ask if I'd decided. i hate that 'this offer is only available on the night' scam. Or those buy one get one free type schemes. I had lots of scare stories from the salesmen about other companies windows and security risks. And lots of hard sell with their finance. All these companies were the big, well known ones.
I decided that I wouldn't do business with any company that needed to use any of the above tactics. In the end I avoided all the big companies that advertise nationally as I found the ones I spoke to as bad as each other.
Like Thing says I found one company that is a family business and has been around, with the same name, for 20 years. The salesman put on no pressure, the quoted price was the final price and was valid for 6 months, he didn't use any scare tactics or bad mouthing tactics or any of the above. And I was pleased with the result.
So now my rant is over, my advice would be to look at a window sample, check the type of locks- mushroom head bolts are better than straight ones, and check the hinge side to make sure it has something to protect the hinges from being forced from the outside. Theres a difference of opinion about internal or external glazing, some say internal is better, but is more expensive and rarer, others say enternal is just as safe. The other thing to look for is the ability to have the window open a small amount and still lock, (I think most do this), and metal reinforcement where the bolts secure into the frame. Some reinforce all round the frame, some just around the bolts.
Other than that, I'd say don't believe any of the offers they come out with, especailly those where you have to sign on the night. If they can offer it that night they can offer it in 2 weeks.
I've since found that lots of builders and carpenters will fit and supply windows, I even found a carpenter who'd fit a window I bought.
Its also worth pricing up from B&Q, you can input the window sizes into their website to get a quote. Though this is for DIY fitting it gives you a comparison.
Amanda