"I called the LBS and they said they don't recommend that because it doesn't last."

Bull****. Properly installed they are stronger than the original aluminum threads and you'll only get them out with a special removal tool. Many military and aerospace manufacturers routinely install Helicoils during manufacture due to their superior strength and wear resistance.

Edit: Unlike the process described above, Helicoils do not rely on threadlocker to be kept in place. They are actually fabricated larger than the tapped threads and rely on an insertion tool to twist them smaller as they are wound into the hole. They then expand as the insertion tool mandrel is withdrawn, locking themselves into place.