I had a pair of Ones as surrounds for my Arc, and replaced them with Era 300s. I love them, but the amount of Atmos content I watch is limited. When it’s there (mostly Apple TV and movies), it’s spectacular, but that amount is currently small. 
 

Thank you very much for the reply. So when watching movies through a 4k player or streaming via netflix would you say they are a worthwhile upgrade to do? Also the rear speakers will be about 3 foot from my head do you think this is too close for the sound they produce? Many thanks for your advice and tips, its much appreciated. 

Surely it’s only you that can assess the cost/benefit? If budget is not an issue, and you want the full Atmos effect when it’s available, then go for it. 

Absolutely agree with ​@nik9669a . I have no way to determine if the value is there for you. As I stated, I love mine.
 

And no, I don’t think three feet is ‘too close’ 

Awesome thank you very much for the helpful replies guys, much appreciated, I think I'll go ahead and get them then and see how it goes, am I best selling my ones or can I use them on their own with a tv in another room? Thanks again all

You can certainly reuse the Ones as a different ‘room’ in your system. Or, sell them, although if you do so, I’d recommend a factory reset first, to remove your information from them. Not necessary if you’re just putting them elsewhere, though. 

Nice to have Sonos in more than one room. I have a pair in my kitchen, you could also do two rooms with one each.

Selling is for your 33rd Sonos, ones over the maximum system limit. :-) 

They also make nice gifts for parents or kids, mom at 101 is still using her One, kids just got my spare Arc and a pair of Play 1s, grandkids (still at home) have mentioned how they'd be happy to remove a Sub too.