You are paying extra because they are Sonos stands. IMO, the Sonos stands look much better because they have a sleeker profile and cleaner lines.

@Rob_95

I use the Flexson stand for my Era300 and it’s really fantastic. High quality and absolutely fair price. But I don’t know if it is available in your region. 
https://flexsonusa.com/collections/era-300/products/flexson-floor-stand-for-sonos-era-300-speaker-white-single

I, too, am a fan of Flexson stands, they support a multitude of surrounds and other speakers in my household. Unfortunately, I’ve not purchased both the Sonos versions and the Sanus versions of the era 300 stands to give you a qualified evaluation. 

@Airgetlam 

Short trip off topic… Do you know the Flexson premium stands? For example for P5 Gen2 and Five… made of a metal, glass and finest wood mix. My absolutely favorite floorstand. 

I went with the plain metal ones, but I do see the appeal of that wood finish. ;)

I opted for the straightforward metal ones, although I do acknowledge the allure of that wood finish. ;)

I settled on the Sanus height adjustable stands.  The Sonos stands were too tall, and Flexson provides no information on the height of their stands.  With the Sanus, at least, I was able to dial in the correct height. 

@Rob_95 

With the Flexson you would get 69,2cm. 

https://www.flexson.de/media/pdf/05/c3/e8/36444_36445_Datenblatt1aXXHXIu7WF58.pdf

Unfortunately the US Flexson distribution site doesn’t show this document. 

I’ve often found the US version of Amazon to be an acceptable place for some of that data, but agree that when I go to Flexson, I usually start with the UK version. 

If cost is an issue then the Flexson is more than adequate plus it has the height adjustment option  model available . On the other hand the sonos stands are premium made and they look it . If money is no object and the static height is ok for you, I’ll go with the sonos branded one . 
 

I have both in two locations .. and the sonos ones are in the “display” room.  The Flexson is more than adequate in the bedroom. 

That's exactly what I did.   Flexon adjustable stands in the bedroom and the Sonos stands in the Livingroom.