Mallet instruments like Marimbas and Vibraphones can differ in the width of the bar. In general, the top of the line instruments will have graduated bars (bars that are wider on the lower end of the instrument and get smaller toward the higher end). The wider bar will resonate more, which will produce a louder, fuller sound. Instruments with smaller width bars or non-graduated bars, work well for entry level instruments and budget conscious schools. These are also great for musicians who are gigging and often play in tight spaces.
Playing mallets instruments has a lot to do with muscle memory. Getting accustomed to your marimba’s specifics is something that will happen over time through all the practicing you will be doing. If you are accustomed to playing on a graduated bar instrument, playing on a non-graduated bar instrument will seem much different. This is a natural feeling, and is something that as players we have to deal with.