My in-laws, in their late 70's, got Senator Windows last year. They were given other recommendations by family members but chose Senator as "they have a good name". The windows were installed on behalf of Senator by a contractor.
Several frames were left loose, i.e. the entire window frame rocked, with unfinished plaster and loose flimsy PVC window boards. Debris was left all over the place, with no effort to clean up.
Senator were told to get another crew to finish/repair the work, however they insisted that only the contractor who put the windows in could do it. Eventually the job was finished adequately (but not to the satisfaction of my in-laws or a builder friend who reviewed the work following the initial install)
As you can imagine, the entire episode was deeply upsetting for them - and they paid top dollar - approx. 40% more than the recommended by my brother-i-l. Other than the "good name", the main reason they went with Senator was that "The salesaman was well dressed and showed us everything on a computer", whereas the others were only tradesmen with notebooks!!
The upshot was the matter was put in the hands of a solicitor, but my in-laws decided in the end that "at our age, we don't want to be spending days in and out of court" and decided to put up with what they'd got.