The trouble is that your online market hasn't caught up with how good these bits are yet - I'm afraid you're chatting to serious, hard-core Mdina collectors here - we know it's an unusual, probably early and very good piece, especially with the amethyst trailing but online all "they" know about are Fish vases and crizzle stones.
You'd probably get more for it in the shop, you can give the info. about it though, send your potential buyers here if you like, to read this.
And try a bit more than the £25, if you've got a good customer base.
It's a serious bit of glass - it will go up in value once folk do realise what it is!
The suggested £25 is to keep it in line(-ish) with the current (low, but growing) collector base for these non fish and crizzle stone bits.
(I used to be an Oxfam shop bric-a-brac "lady" - I know getting this sort of thing both right and getting it sold is not always easy! Good luck!
And clean it if it's mucky. You get better prices for clean stuff. :thup: )