They are pretty reliable. However hold off on buying and get some hands on
For paintball purposes the 'real gun' layouts are not the most efficient, the 'bling' style guns are the ergonomicaly correct design, and the Sierra is based on an old design.
However that does not mean they are right for an individual. A lighter ergonomic speedball gun may be the optimum, but if it feels wrong for you then it's not for you, and for some people a light gun is too light.
Are you looking at the Sierra because it has the looks you like, and also regarding your plans for it do bear in mind that a number of items people add in paintball don't realy add any benefit.
Rails etc on the 'tactical' guns only realy benefit with the ability to mount a camera (which ought to be your second camera as a head mount will give more footage) and a torch which is good for the night and indoors cqb games - as long as the user knows how to use it and maintain light discipline.
Sights don't add much, paintballs don't work that well for sights, you can't use the sight properly wearing goggles and your eyes will be too far back for most sights. Red dots can have a use, such as when using a gun with a central hopper and placing the sight behind the feedneck. But if you practice you can get the optical illusion of seeing through the feedneck and don't need the red dot
A telescopic sight can be good when accompanied by a camera to give zoom 'kill shots' rather then for the aiming, or with first strikes but only if you have tuned and practiced a lot to know where to view and adjust etc
ah well seen a few more events I'm up for.