I had couple of those MT500 overshoes. Good thing is they keep Your feet warm, the newer version does not look like some funky wellies, my second pair had a problem with the velcro thingy, strong velcro, cr4p glue
They were not as breathable as my current MW80's, good thing was they covered shoes from mud etc, however they will probably last only one season, and at £25+ a pair might get expensive. Also they are not waterproof from the bottom so they will let water in if You stand on some soggy ground. However top is pretty waterproof and never had wet feet with them. Good thing is they are much taller than the neoprene cuff on my winter boots so cover more from water.
My MW80's were only £80 (size 47 feet ;-)) and will be used for the second winter this year. Still look very good. Only had cold feet at -5 on a longer ride once. Dry quick, they never let water in through the main shoe or from the bottom, but the neoprene cuff is only water resistant and it will let water in after some time, when it's really pouring down I've got overtrousers over them and it's not really an issue.
If You're planning on riding a lot during winter and won't like the faff of taking the overshoes, than the shoes etc than winter boots will be a good choice as if they last 2 more winters they will be the same price as 3 sets of MT500's while being much more convenient to use.
So if You want overshoes MT500's are a very good buy, lasted twice as long as some adidas or northwave I had before. However if You can get proper winter boots at a good price than I would go that way. Buying the MW80's was probably best £80 I spent on bike kit. My mate uses seal skins socks during winter but I would still prefer overshoes at that price.