I've been making and using partial capos for 30 years: 2-string, 3-string and 4-string capos. The most useful for me is the 3-string, which bars the E, A and D strings, and leaves the top three stings open. No commercial manufacturer I know of make ones that will work when you lop that much off the end of a capo. The capo tips up and the low E string buzzes. (I've hacksawed virtually every brand of capo ever made, so I know!)
The only 3-string capos that works closes above the strings, not behind the neck. I make 'em to order from capos I order from overseas.
Glenn