Pros
UL affords a great work/life balance. Flexible schedule with the ability to occasionally work from home makes it easy to balance responsibilities at home with those at work. Coworkers are genuinely friendly and easy to get along with, even those in management. Used to be a monopoly in the industry until newer companies caught them sleeping and took away market share. Now they seem to have their act together in terms of future goals and planning to regain market share. Your day to day work, though monotonous, helps protect consumers from unsafe products.
Cons
Change, Change, Change. As I said, UL is working hard to regain market share while branching into new markets. Oftentimes, this means changing things just for the sake of changing. Many ideas get implemented without thoroughly thinking through the immediate impact, and many ideas get abandoned within a few weeks. Seems like every few weeks, there is a complete retooling of work flow processes and systems. On a day to day level, work can become monotonous. For engineers, not much technical skill is required (though communication skills and ability to explain technical concepts are very important, which is a pro). Hard to figure out the basis for promotions and raises. Salary is on the lower end of the industry average.