Trimmers can sometimes cost an arm and a leg. Well whether to buy it or not is your decision but do consider the following:
1.Trimmer is obviously a more professional tool as compared to scissors but you can have more control over the scissors than you can in case of the trimmer
2.You may or may not know how to use a trimmer and may end up buying one to realize its not your cup of tea. So if you are good with scissors or willing to practice scissors first then go for it.
3.Trimmer are definitely easier to use as well as clean and maintain. Scissors may get rusty or blunt or you may snip off the wrong patch. Trimmers are definitely more professional
4.When it comes to travel, scissors are an easier option because they are light and also trimmers need electricity or battery which may or may not be available plus it will just make your bag heavier.
5.Trimmers are a one time investment. If you get it right and can work with it then you are good to go for many years to come. It may just need some maintenance but nothing more!