Just an update. I downloaded Viewranger this morning & used it today. It is absolutely awesome & very accurate. I went for the premier one at £9.99 which comes with 1000 credits (usually £14.99) I downloaded 4 tiles so far, and was amazed at how much you get. I still have 834 credits left, but will just download new ones as & when.
I rate it highly & am glad that I asked the question on here first.
Thanks guys !