Even though Simonton does manufacture new-construction windows, most of the questions that come my way deal with replacement windows, I'll assume that's what we're discussing. Replacement windows go in existing homes; new construction windows go in new homes or additions to existing homes.

In short, Simonton is fine to purchase.  Three data points to remember:

1. Simonton Does Only Vinyl.  Simonton windows are all vinyl windows.  While never the classiest type of window, vinyl windows are last forever and never need to be painted (the flipside, of course, is that you cannot paint vinyl windows with much effectiveness).

1. Long-Established Brand.  Simonton brand has been around since 1946, pretty much in the same form. It's part of Fortune Brands Home & Security, which also include Master Lock, Moen,, and Therma-Tru. All trusted names.
2. Well-Represented.  Lots of replacement window companies push Simonton; this is no outlier brand, by any means. According to a J.D. Power study, Simonton has a higher overall customer satisfaction rating than Pella or even Andersen. Because even though defective windows go straight back to the manufacturer in the form of a warranty claim, the installation companies administratively bear the brunt of this; it makes their job easier to install flawless windows. Reportedly, Simonton has a well-oiled distribution chain between it and the retailers, which means that retailers get windows faster and with fewer problems.

Like many other window manufacturers, Ohio-based Simonton is continually improving the quality of its vinyl windows. In days of old, "vinyl window" was synonymous with "bad." No longer.

It's possible to buy pricey vinyl replacement windows, too, so be careful when shopping. This applies to all brands, not just Simonton.

You're going to be buying Simonton windows through authorized dealers, not directly.
I know of no reason not to buy Simonton windows. If anybody has any reason, let me know.