@PoP: Yeah, now that I have a K3 plugged in, indeed, can't slice on the K3 busybox version, but I seem to remember it working on newer models.
Which is likely, given that it's not a bb limitation, as it works in my own bb build (which you could always resort to, I guess ;p. Which would logically lead to the next step of simply using ZSH ;p).
Code:
[root@kindle root]# BLAH="ABCD"
[root@kindle root]# echo ${BLAH:1:1}
-sh: syntax error: Bad substitution
[root@kindle root]# /mnt/us/usbnet/bin/busybox ash
[root@kindle root]# BLAH="ABCD"
[root@kindle root]# echo ${BLAH:1:1}
B