the problem with all national chains is who fits the windows, a good anglian fitter will be as good as anyone else, a bad one well…
Plus points you should get a guarantee that is worth the paper it is written on, they are less likely to go bust than many of the small one man bands.
Anglian used to be supplied by http://www.gbwuk.com, if the sales director was ever in a car crash i would quite happily pop to the local garage to get some petrol and marsh mallows. Be more useful toasting marshmallows than anything else.
The panels themselves are fine, just the business.
Just a few points, watch for dark colours on south facing elevations, heat build up can be an issue frames can and do warp if badly installed.