I still use it on lp's that I expect to play a lot, say 8 or 10 times a year. But I'm very careful with it, and only apply it while outside the house - for reasons stated below. As far as a sonic signature - I don't hear any difference that could not be attributed to an overactive imagination.
However, the effect I would worry about is your health. I am not aware of the EXACT formulation - but I know that LAST is basically a "Flourinated Hydrocarbon" such as PFOS or PFOA which they originally sourced from 3M. (3M shut down production in 2002 over health liability concerns). It's contact basically turns the top few molecules of the LP surface into Teflon, which to oversimplify - is created by exposing Nylon (which includes viNYL) to a Fluorinated Hydrocarbon gas. Your new Teflon record is much slipperier and heat resistant then before, so it doesn't wear out. However:
Here's a quote from this website: http://www.ewg.org/reports/pfcworld/es.php
"The U.S. EPA peremptorily forced one member of this family off the market in 2000: PFOS, the active ingredient used for decades in the original formulation of 3Ms popular Scotchgard stain and water repellent. Shortly thereafter, 3M also stopped manufacture of a related perfluorochemical, called PFOA, that is now under intense regulatory pressure at EPA. 3M formerly sold PFOA to DuPont, which has used PFOA for half a century in the manufacture of Teflon. (DuPont now makes the chemical itself at a new facility in North Carolina.)"
Here's a quote from the EPA:
"PFOS accumulates to a high degree in humans and animals. It has an estimated half-life of 4 years in humans. It thus appears to combine persistence, bioaccumulation, and toxicity properties to an extraordinary degree."
- May 16, 2000. Phaseout of PFOS. Charles Auer, USEPA, Director, Chemical Control Division Office of Pollution Prevention and Toxics (OPPT)
Hope I'm not depressing anyone - my knowledge of this is incomplete, so it might be nice if someone from the Last Factory could clarify the risks. But I'm worried that a full disclosure wouldn't quite be in their interests.