Hi aaargh,
How do you fit coving around a completely curved alcove? Probably with great difficulty.Will it be a plain or fancy coving? Either way,I think it will be a fair old tackle to try to get it to bend around a completely curved alcove.I don't know the product that you mention from "Arthouse" that is made from Duropolymer,so I can't say whether it is, as you say, "bendable".You could always contact them and ask whether it would be suitable for your alcove.Plasterboard coving,even dampened,would probably be difficult enough to bend around too,and then you have to fix it in place,again,that's if it would work. If the coving in the rest of your room is just the plain shape,and is made from either plasterboard or plaster,you would probably be able to get someone in locally who would be able to run the coving around your alcove in situ.That's all the comment I can make.Good luck.
Regards:Roughcaster.