The ones listed below are all soprano models. I measured the width of the fretboard with calipers just this side of the nut.
Kala KA-15S: 1.362"
Kala SMHS: 1.365"
KoAloha Opio: 1.400"
KoAloha Pikake: 1.510"
I find the 15S just as easy to play as the Pikake, even though they're on the far ends of the spectrum. I find the SMHS the hardest to play because I tend to have the A string roll off the side of the fret. I initially thought it was the neck width that made the difference with these until I got the calipers out. Even though the 15S has a narrower neck width than the SMHS, the nut spacing is more narrow on the 15S and as such, I don't have the string roll-off issues. Nor do I find the string spacing too narrow, and I do a lot of fingerstyle playing.
Measuring the nut grooves from the inside of the G and A strings, the spacing on the 15S is 1", on the SMHS it's 1.070". That extra .070" spread with only .003" extra width on the fretboard is very noticeable to me. Knowing this, I can change out the nut on the SMHS and have a much more playable uke when I'm done.
As far as UK prices on ukes, I'm clueless. But I would say to keep an eye on not only neck width, but nut string groove spacing as well.