Martin C1K is the first ukulele that I bought with my own money (previous ukuleles were borrowed from relatives). It is still my favorite concert ukulele that I own, though I do not own any concert ukuleles that cost more than $1000. I have tried a US-made Martin concert ukulele at the local Martin dealer and that did sound noticeably richer than the C1K, but the price was 3 times as much, so you do get what you pay for.
Price of the C1K in the US is USD $499, which translates to less than £400 UK pounds. The value may not be so good in the UK where the retail price is £545, but I think the value is great for a real koa concert ukulele sold in the USA. I do like the bright sweet koa sound.
My only real complaint is that 12 frets to the body does limit my playing style a little. Most concert ukuleles (and even some sopranos) have 14 frets. On the other hand, the C1K is lighter weight than most concert ukuleles (less than 1 pound in weight), which makes it easier (for me) to play.