[Mod: Please note that Paul's decanter shown in this post has been agreed as "not the Waterford pattern". Rather than attempt to modify what is a useful discussion, please see the new thread that Paul has created for this decanter - for which somebody may eventually be able to give a pattern name.]unfortunately, we didn't see a picture of David's other decanter, but always possible it may have been the same as the attached example.
At least I think this one is 'Waterford' - there seems to be some variation in what might loosely be described as a butterfly outline - a large rectangle with a substantial mitred cut within each of the four segments, producing a sort of 'four wings appearance'. Of course, if someone knows it's some other pattern shout quickly.
The backstamp is simply the word Stuart - no England - and the final t has a Wrigley tail. In view of the lack of staining, base wear and overall condition - combined with the type of backstamp, then I'm going to suggest the date of manufacture is around 1950 - 60.
It will no doubt go back out to the charity shop very soon, but for £2.99 I couldn't resist it.
Not sure what David meant by 'the same normal shape' - decanters vary enormously in design and shape - I was tempted at first to say my one was a form of bludgeon, but now not sure, and it could even be something rather obscure called a 'Taper-globe' - an Anglo-Irish form made originally c. 1800 - 1820 - a hybrid derived from the taper and shaft-and-globe. But I'm taking a bit of a punt and could be well of course.