Hi,
One of the things you will need to consider when buying binoculars is how will I use them. Size and weight are as important as optical clarity and magnification. I have two pairs, one pair is 10 x 50 the same as the ones you are considering (that's 10 times magnification and the front element is 50mm in diameter) but they are large and heavy and as a result I don't use them much.
The other pair is 10 x 21 which I use much more as they are small enough to fit in a coat pocket and light. Currently on sale at Argos and well worth �10.
http://www.argos.co.uk/webapp/wcs/stores/servl et/Search?storeId=10001&langId=-1&q=BINOCULARS &pp=20&c_1=1|cat_8963346|Clearance%20photograp hy|9716428
The size of the front element determines the brightness of the image ( the larger the front element the more light is available for you to see). To be honest in daylight I cannot see much difference in the image brightness between the two pairs I have, even though the smaller pair is half the diameter of the larger pair. Only when the light is fading towards dusk can I tell the difference, so this is another point to bear in mind when choosing your binoculars.
The best thing to do before buying is to find a photgraphy shop or outdoors shop where you can try different sizes side by side so you can not only see the difference but feel the difference in weight and balance as well. As I said earlier if you intend to take them out on walks with you a small light pair will probably suit you best.