In reply to duckweed:
Charmoz and Manta are built on different lasts so the fit will be different. have a look at scarpas website for details. THey hae changd a bot over the years as well.
Mind you 300 quid aint cheap, 2nd hand boots are often sold not due to wear but poor fit...if you bought a 2nd hand pair of boots you could sell them on (like i did with my nepals) - went back to scarpa for fit, without a big hit, but it's your call.
re crampons - if you want to get one quality pair, something like Petzl Lynx is very versatile, dual and mono, cradle and clip, top notch product, adaptable to your boots. I have an unused pair as I changed my mind and have a few pairs rigged for different boots instead ( i should sell em)
Good luck