Many people were still practicing visualization in the present-day and a lot of them have chosen Xuanwu as their external visualization target.
After all, the leftover records of visualization found in the Spirit Library taught the method by using this deity as a sample.
Once a person had attained visualization, he could then focus his mind. The method could help in clearing his thoughts while further mastery could help in stabilizing his mentality to prevent interference by bewitching illusions.
Although visualizing Xuanwu was a good option, the troublesome part would be the target being too high a level to achieve.
There is a saying that 'the heart usually has ambitions too high that life is too short and fragile to achieve'. One should always work within one's capabilities. If a person had average potential but tried to visualize something as grand as an emperor deity, this would be overestimating one's abilities.