This one has been puzzling me. I have difficulty with the Poli attribution, mainly because so many are incorrect that if a real one came along, well, I'm not sure I'd pick it out. Also, I haven't handled much of this glass; it's price is way out of range for the large majority of the collectors on this board.
At the same time, on p. 190 of "Murano: Glass from the Olnick Spanu Collection" is a sommerso piece by Poli which is described as "transparent grey sommerso in cristallo glass." The piece is in the Valva collection so the shape is different from your piece (it has a very wide mouth, but it is a flattened oval).
Your shape is closer to the vase pictured in Pip's trip, but who is "Arte Nuovo Murano" and why wouldn't a Poli piece have a Seguso Vetri D'Arte label on it?
The reality is that after Poli won the big prize at the 1954 Venice Biennale, you can be sure that many companies copied the style, and if he did a piece in transparent gray, you can bet other companies did as well. So I take back my assertion that this isn't Murano. It could be Poli, but more likely Poli-influenced. I think you'd have to take it to a high end dealer to have any more certainty than that. A very interesting piece to have, then.
David