Sorry for bumping...just my two cents...
We have one, but it is not the most heavily used piece of furniture in the house. It's in the study, so that one of us can be reading while the other is on the Internet or doing desk work, i.e., we can still be in the same room for conversation. Although it's one of the less expensive models, it is wonderfully comfortable.
The main price differences are due to the amount of padding from one model to another, and the grade of leather in which you choose to have it finished. Also, some have attached headrests or headrest pillows. Unless the manufacturing policy has changed, some (all?) models are also available in microfiber cloth upholstery rather than leather.
One of the main advantages of the product line is that most of the models come in a choice of sizes, so that it's possible to match the model to the size of the person most likely to be using it. For example, the Diplomat, Consul, and Ambassador https://10restbest.com/best-zero-gravity-chair --still the least expensive models, I think--are all the same shape and have the same stitch pattern on the upholstery but are different sizes of the same chair for different sizes of bodies. . . . If multiple people will be sharing a single chair, however, it is generally best to pick the size appropriate to the largest person, i.e., largest basic body frame size. My wife is petite but still quite comfortable using the larger Ambassador.
If searching online, Stressless is the U.S. product marketing name, but also look for "Ekornes" (Eh-kor-ness), the name of the Norwegian manufacturer. They do have occasional national sales, but not on any predictable schedule, or at least none whose timing I've been able to figure out.
We bought our chair from Recliner Store, the online name of a furniture store in central Massachusetts. I usually try to "shop local" and would have been glad to buy it from a local furniture store with whom we'd done business for years, but they would charge a $65 fee to transport it three miles to our house, whereas the place in Massachusetts offered free delivery.