There are many different size rollers. It is quite possible you are using one too large for the groove in the screen frame. When you roll the spline in make sure you have the roller parallel to the frame. If you twist or angle the roller any way there is more chance of tearing the screen material. And go slow. I find if I rush too much I tear screen. Also check if the frame is straight.
Another thing could be that the spline you are using is too large for the groove.
Fiberglass is for sure easier to work with. I do not like working with aluminum screen material and only re-screen with it if a customer insists (which is very, very rare).
I haven’t found that people want aluminum more than fiberglass, in fact I have noticed people don’t even know the difference or what they even have in their windows. Why do you think you have found that people like aluminum over fiberglass?
I bought mine from this place. It seamed like a good idea but I rarely use it, I usually just use the roles of holes to make sure the frame is square. I will use it to straighten out frames with minor bends in them.
I saw this yesterday while searching the web for screen jigs. Some places sell the same jig for twice as much as the link you posted.
So far I’ve been doing screens on site minus any kind of jig system. (I really haven’t done a lot of screens to date) I’m sure with a lot of frames and especially smaller ones it would take more time to set up the rig than to do without. If ever I feel the need to have one I’ll probably make my own.