I used to have one on my Curve 8330. The product was of very high quality and came with the necessary solution and tool to effectively apply it.
However, I found that after applying it, having followed directions to a tee and actually reapplying it a couple times, there were some air-bubbles that were next to impossible to get out. The screen added an extra gloss that made the phone annoying to look at, and after constant re-holstering and use, the edges started to accumulate dirt under it that looked like grime.
There were also areas on the phone that were very difficult to effectively apply the film and have it stick without little pieces of it hanging off.
Granted, I tried the key tests, the pen tests, tried to destroy the phone on the surface, and as long as that screen was on, it seemed impervious to cosmetic defection.
I'd a good product, but if you are OCD about cleanliness or imperfections, not a product for you.
"He that hath no sword, let him sell his garment and buy one."
Jesus, Luke 22:36
"The deadliest weapon in the world is a Marine and his rifle."
Gen. John Pershing, U.S. Army