I'm a slime tube user too. Goatheads, glass, catclaws all lurk in the paths I cannot avoid. Have used the slime tubes for 1 1/2 years with great success. Tips:
Park your tires with the valve in the 10-11 o'clock position. If something is trapped in valve, unscrew the valve (ask for tool from LBS - mine was free). Clean out any small rocks or old slime. Rescrew the valve (important step). Park in correct position to let slime slide to bottom. Refill.
My LBS guy said to let the tubes heal themselves after a flat, then reuse. Works for me. He said the only time they are beyond repair is if a nail goes through both sides of the tube.