Because I know almost nothing about Sommerso glass, I can only look at this thread with interest and wonder why there are reports of these style vases being seen in some numbers in fairs and gift shops (UK only??).
From the link that Otis has given to the page in the Talismanlondon site, I clicked the "back" icon and looked at the other sommerso items they have available. I am intrigued that there are several examples of cut and faceted pieces and just the two of the type discussed here. Also, I notice that the two in that website are described as "a pair" and "30cm height" but they are different colours and clearly different sizes.
With my Moderator hat on I will move this thread to the Murano forum and hope that others who may not have seen this will be able to comment.