Rollers are a bit tricky to learn to use and most models don't provide any serious pedaling resistance. Some do by using small diameter rollers and/or by adding a resistance fan but they are in the minority. Rollers require your constant attention while using them and a wandering mind can launch you right into the nearest wall. They do improve or maintain your bike handling skills.
Stationary resistance trainers that mount your bike on them and use a fan (effective but noisy), magnetic resistance (quiet but too linear) or a fluid resistance unit (quiet and realistically non-linear) to provide a work load are generally more effective at providing a workout but do nothing to improve riding skills. The upside is you can watch TV, movies, etc. while using them which helps compensate for the incredible boredom they produce.
I have a Performance house brand (Travel Trak) fluid trainer I use when the weather is too nasty to ride outside. About all I can say in defense of any of them is that it's better than doing nothing.