They're better at moving and shooting than blowpipe skirmishers, but get less shots. The shield rarely comes into play, but the ability to stand and shoot allways sure does.
They can but since javelins are quick to fire they can stand and shoot even if theenemy is too close for normal stand and shooting, makes for great screening units.
Javelins out perfrom Blow pipes every time I take them. With Jav being range 12 this addition there is not down side. And quite often you will be hitting on 5's so you actually get a few more wounds in. at 3k points I like 2 units of 18 skink w/ javs and 2 units of 10 chamalien
I mostly use the jav for my skink priest squad. Shields make them a little more durable and always being able to stand and shoot is always a bonus.
I exclusively use stick-and-shield skirmishers, primarily because, being quick to fire you don't take penalties for moving. This is a tremendous advantage compared to blowpipes. With a potentially 24" range, javelins let you drastically compensate for the otherwise limited range nature of your infantry (or your forces in general). Yes, they won't potentially kill as much, but the number of things you can do with them drastically rises. The shields are merely a bonus.