As already stated if done correctly a tear aid repair should last indefinitely.
I repair kites and wings here in WA and also try to offer options of repair or replacement. Where it's possible repair is cheaper but some customers prefer new.
In my opinion the limitations of tear aid are determined by the width of the blowout - tear aid is better as one large piece with no overlaps as air can escape where multiple layers of tear aid meet.
Getting it laid flat is essential as any creases from the hole to the edge will cause a leak and if there is overstretched material around the rip this should be cut away and a backing put inside to prevent the tear aid sticking to the other side of the bladder.
Tear aid is available in 3" and 6" wide rolls so bear that in mind when ordering.
Also note that tear aid adheres better to some brands bladders than others. Fone is fine but I have found duotone bladders have some issues and require a bead of glue (stormsure or pu glue) to overlap the tear aid onto bladder to double secure the patch.
Hope this helps and clears up a few worries you may have
Ryan
The Sail Doctor
Wing and kite repairs