Liner locks were first invented and used in their present form by Michael Walker, a very famous high-end custom knife maker. Done properly, it is a very safe locking mechanism. Made poorly or wrong, it is next to useless. It is probably the most common locking mechanism used in folding knives in All prices ranges, both production and custom.
There are many other variations of the locking folding knife: integral side bolster locks, the Axis lock, the REAKT lock, the traditional back-lock and front-lock, Bill Peases's front side lock, and Scott Sawby's 'self-lock', just to name a few.
There is nothing inherently wrong or bad about liner lock designs. But they can be done well, or poorly. Putting trust in a poorly made liner lock mechanism can risk fingers. But that is true for Any folding knife lock. Some are better than others.
Paracelsus