I run a Hope V-Twin converter.
Got Ultegra 10sp STI levers running cables through a set of Specialized own-brand bar-top levers and from there to the under-stem converter. Works well but it has to be said the brakes feel horrible – very wooden. It’s due to the massive extra friction with that routing through the bar-tops and the very short, tight curve from them to the converter.
After the Three Peaks I’ll probably remove them. That said, they’re very good not just for the extra control on descents but also as a braking option when just pootling along on canal towpaths etc.
I think you will find that you lack control. The drops are always going to be better for control on rough ground as the tops are dead narrow.
Yes but factor in the need to get your weight back when doing steep rocky descents – being in the drops just makes it more likely you’ll go over the bars. Bit of a balancing act between braking efficiency and control.