Reporting back with my brother's thoughts. He is a Monart collector and knows a lot more than I do. I'm just familiar with all his stuff.
He would like me to make it clear that this is opinion, it's not backed up by documentation, it doesn't exist.
"The cloisonné is very rare and big! We have a smaller one and I don't recall seeing another - the green is not a trick of the photography - I'd say it wasn't the same as the colourway on Scotland's glass. Red is far more 'common' if you could describe cloisonné as being common, that last bit to sell was an unusual shape though. Surface decorated bits all tend to be early (not sure if this is documented anywhere) - they were probably the 'Monart Ware' period but without a label you can't prove it. Monart Ware stopped around 1929 so only lasted a few years. Pieces were only made by the Ysarts - and it wasn't their day job!"
So, educated speculation would date your vase to "pre-1929".
And you can use the word "rare" with confidence.