I used to use slime and I had no flats for a couple years and forgot it was there until I went to let air out to change the worn out tires.
I started using it when I went to Arizona on a bike trip in the early '90s... On one desert ride four of us started the ride, two of us has slime in out tubes, and two had to walk back to the trailhead.

THe trick to using slime in presta tubes is to cut a small slit in the tube when it is off the bike, squirt half the bottle in (being careful not to make a mess), clean up carefully around the hole, then patch the hole with a regular vulcanizing patch.

It might be better to figure out what is causing all your flats and then solve the problem if possible.