Cheaper it may be, but it is only designed for one cable up to 10mm² to be connected.or this:
http://www.screwfix.com/p/volex-cooker-outlet-plate/50538
which is considerably cheaper, and a recognised brand.
The dual connection plate (linked to on eBAY) is made by Click Scolmore.
A more quality make than Volex I would contend - and also made for the purpose of connecting two different CSA cables!