Downtube shifters do restrict your shifting and induce a greater range of
cadence than most brifter users find comfortable. On 8spd and up bikes
with brifters you are changing gears constantly in response to minor
changes in grade because it is so easy to do, just flick the wrist and your
done. When cruising along it is no big deal to take a hand off the bar reach
down and shift, but with friction you have to hold a bit, a few seconds to
overshift slightly then readjust the lever for minimum cage noise. When
accelerating or jamming up a hill that loss of attention can be such that for
many riders it is easier just to stand up or accept the reduced cadence and
increased torque. Brifters are thus a whole different ball game and way of
riding except for just cruising around on a Sunday afternoon with the kids.