Statistically speaking children are not injurred by falling off the trampoline so really a net is not the safety feature you need. Children are injurred on trampolines by having more than 1 child jump on the trampoline at the same time.
We had a trampoline when my kids were younger. With proper supervision and the 1 child bouncing on it at a time, no injuries. I work at a school and in the last 3 weeks have seen 2 kids in casts and yup, it was a trampoline accident and yup several children were bouncing on the trampoline at the same time.
The mat is pulled super tight by the force of a bounce down by 1 kid, when the 2nd kid hits it as it is that tight, its like hitting cement.
Good luck, we had lots of fun with ours, the Easter bunny brought it..heard him swear as he was pulling those springs to fit in the dark of the night.