I use custom visuals every now and then, some are absolutely fabulous, others cause(d) issues.
I found that if you use many chicletslicers in your report, massive delays in refreshing the pages will occur.
A report in progress became slower and slower, eventually it took 9 seconds to build up a page. After some testing in Dax Studio, obviously assuming there was a mistake in a measure or so, I noticed that the chicletslicers started blank and then appeared one by one. After replacing them with the standard slicer, the report refreshes in a blink of the eye. Lesson learned.