Hey SMWAM,
It all depends where abouts the tear is. Generally, small tears mid canopy to the trailing edge aren't too bad, but anything in the forward half of the kite should really be repaired by a professional. Products like tear aid and the sticky non stretch stuff we use are great and will certainly get you out of troubl for a few weeks to a season but it is always better to get a repair done properly for peace of mind.
A small tear in the wrong place and a bad crash which loads in the wrong spot can turn a hole the size of a 5cent piece into a two piece kite.
If you are going to do the repair yourself, make sure you do it properly. Ie, use a mild detegent and warm water to wash the effected area on both sides of the kite, then rinse and dry COMPLETELY! Then cut your patch and stick it on making it 1inch bigger radius than the nearest part of the tear and with rounded corners.
As I said, depending on where it is, it will last a long time but it is always better to get sticky back sewn onto the kite to do it properly.
Here's a link to repair advice
www.kiteboardingschool.com.au/index.php/beginner-newbie-tips/tip-20-simple-repairs-to-the-canopy.htmlCheers,
KH