I still use downtube shifters, but went to index from friction in 2015. I have used STI’s and they are better, but downtube can be fun. They work well with a triple crank and massive gear changes can be down quickly.
I changed to index for those times when transitioning from downhill to a quick out of the saddle uphill and hitting the downshift perfectly. As I’ve gotten older I need more of a downshift and I wanted the shift to be there.
What I find interesting about downtube shifters is the right or left hand shift technique. I learned to use my right hand for the right shifter and left for the left. But there are those that use their right for both and reach across.
John