Take musicians. The 10 extra points per unit can save the unit and / or make it useful for an extra turn or more per game, which is totally worth it. This is due to the feigned flight rule. They regroup more readily if they flee, and they can march on a turn after they rally, allowing you to put them into an effective position.
Pistols will not deal out crushing damage, but can plink away at units or potentially kill light units, as others have pointed out. Sometimes taking a wound or two off a unit matters.
Pistols
can win the game for you. My 100 point unit of pistols, or even the one surviving member of a pistol unit, can annoyingly interpose himself between an opponent's best combat unit, and the flank of one of my units, sacrificing himself to redirect the enemy unit, and there's nothing they can do about it! This can decide combats, and win the game for you.
I write my pistols off before the game begins. I take two units in my current list; one on each flank. They have all died on the first turn against some armies, and against other armies, they've decided combat engagements in my favor. They almost always die by the end of the game, but generally they get an opportunity to sacrifice themselves to benefit one of my more deadly combat units.
They are an excellent utility unit. They can redirect, march block, flee to cause a unit to fail its charge, hunt warmachines, kill lone characters, attrit enemy units (even armored targets), kill chaff, charge-bounce fleeing enemies, give cover to your other units from missile fire, etc. There's also the trick below:
The pistols charge the rear enemy unit while your combat block engages the enemy chaff/speed bump. You resolve the speed bump fight first, overrun into the rear enemy unit, and fight a second fight with your combat block in a single turn. Even if the pistols wouldn't stand up in a fight against the rear enemy unit, they let you potentially clobber two enemy units in one turn.
Given that I don't take them to cause serious damage, and given that I expect them to die, I don't take the Outrider with repeater pistol. Even though it increases their damage output, it makes them pricey for a chaff unit.
The only other real chaff units the Empire has are detachments of archers, or cheap hero characters. And while archers are cheaper, the fact that pistols are fast cavalry makes them much more useful, in my opinion. While pistols can win the game for you, you don't build your army around them. You need some halberds, knights, greatswords, demigryphs, or steam tanks to stand toe-to-toe with the enemy. The pistols support these units.