In short, yes. The COMLEX is different enough from the USMLE in enough ways that a dedicated question bank (QBank) is necessary.
Here are a few reasons you need an extra QBank when studying for any level of the COMLEX:
1. COMLEX has a different user interface.
The user interface is very different between the USMLE and COMLEX. While most USMLE style question banks emulate the NBME user interface quite well, this does not translate well to the more limited COMLEX user interface. You need practice with as close as to what you will actually see on exam day to feel as comfortable as you can. A notable difference is to find a question you marked on the COMLEX you must jump to a separate screen, whereas on the USMLE you can simply scroll through on the side bar.
2. COMLEX questions are different than USMLE questions…in content.
While the breadth of knowledge you need to master for each exam is similar, there are enough subtle differences between exams that you should see questions that cater to these differences. Some COMLEX-specific topics include legal principles and OMM. Microbiology is also stressed on the COMLEX and biochemistry is not very high yield, as compared to the USMLE.
3. COMLEX questions are different than USMLE questions…in structure.
COMLEX questions tend to be shorter and leave out details that are not integral to answering the question. There is a recent trend away from these distinctions, but overall they still hold true. Also COMLEX questions now imbed normal lab values into questions, obviating the need to look back and forth between a table of values.
4. COMLEX questions are different than USMLE questions…in format.
Questions on the COMLEX also have a few unique formats that you will not see on the USMLE. These include matching type questions, as well as extended multipart questions, during which your answer choices are not locked in and you are free to move about the questions as you need. There are also distinct audio and video type questions, mostly detailing physical exam type findings.
5. COMLEX has a different format.
Lastly, the COMLEX has a different overall format. The blocks are in sets of 50 questions, which leads to different pacing while working on timing. This is extremely important, especially if you struggle with timing on exams.
Which one to use?
There are two major Qbanks out there for the COMLEX: Combank and Comquest. They are generally overall considered equal. I tend to recommend Comquest, as I think their questions and explanations are of higher quality, and I think the user interface is more intuitive.