Yes, any combination of 3 One or One SL can be bonded as surrounds.  Once they are surrounds, they are semi permanently bonded to the Arc, and they will play music on the Arc and surrounds as a single room.  You can adjust the surrounds to play full volume or ambient for music sources.  

You should be aware that when bonded to the Arc as surrounds the voice control on the surrounds is disabled, so you don’t get any benefit from using Ones instead of One SLs.  (Unless you do regularly unbond them to use them standalone, but I think you would soon tire of that.)

Thanks, you provided me the answer I feared to read: once bounded to ARC I have to unbound every time I want to use the ONE for streaming Music.

Reason to use ONE vs ONE SL is just cost: on Sonos.com the ONE “second hand” cost less than a new ONE SL…

I think you misunderstood his reply. You can still stream music to the ‘room’ that contains the Arc and the surrounds, but you get music from all speakers, not just the surrounds. There is also a setting in the controller that allows you to set the surrounds as ‘ambient’ support for the Arc, or ‘Full’ stereo speakers in addition to the Arc. 

But yes, in cases of surround speakers, cost would be the significant reason to use the SL rather than the standard One. 

Since I occasionally change around my various ‘rooms’ and swap out which devices are considered ‘surrounds’, it makes more sense in the long run for me to choose Ones, but not everyone does what I do, so if you think they’re permanently surrounds, the One SL is the more cost efficient. 
 

Many thanks for your clarification!

 With regard to cost, indeed … The ONE cost less than ONE SL! Look here: https://www.sonos.com/it-it/shop/certified-refurbished?ds_rl=1255708&ds_rl=1256426&ds_rl=1256480&gclid=EAIaIQobChMI47nd5aaH9gIVmrp3Ch0e3gpEEAAYASABEgKnpPD_BwE&gclsrc=aw.ds

But as you said yourself, it is not a comparison of like.with like. But I understand the motivation for your question now