Is this board any good?

First it is NOT an AM3+ MOBO, it's the more current regular AM3 socket -> http://www.msi.com/product/mb/870A-G54.html#?div=Detail it seems aria.co.uk is wrong.

Currently, MSI only offers the AMD 990 & AMD 970 chipsets with AM3+ socket support. http://www.msi.com/product/mb/#/?sk=Socket%20AM3+

Otherwise, for your budget it's good   The AMD 870 chipset supports (x16/x4) which means the Primary GPU is getting the full x16-lanes but a Second GPU gets x4-lanes of PCIe. So unless your plans are to install 2 expensive GPUs in CF {Crossfire} you're fine.