Tuffy does not weigh much, but the weight is placed in the wost place, rotating at the rim of the wheel (see angular momentum).
You can stop every 5 mi or so and check your tire for embedded glass ect. Tuffy probably buys you an extra 3 mi before you get a flat. Slime works for things like staples.
If stuff is embedding in your tire it is either cheap to begin with, or old and has lost it's elasticity.
Tuffy can also cause flats by pinching the tube and eventually making a hole.