*UPDATE* The Power BI Update team has resolved this problem. To read about how Power BI Works now, check out my blog post Time to Use Custom Visualizations in Power BI.
After looking at some of the neat custom visualizations with Power BI, like the fish or something like the synoptic panel, I was sold. Time to start using these neat visualizations in my reports in Power BI. I rather regret the decision. Why? I’ve provided my reasons here.
Warning Messages Every Time the Power BI Report is Viewed
Neither I nor the client is interested in seeing a message which looks like something sketchy is in the report. Reports are supposed to answer questions not leave people wondering what is wrong every time they look at the report. 
The message looks like some kind of a legal cover just in case the code is really bad. Worse the report is broken as the visualization will not show until the yellow button is clicked. Yes I can click on the button and the message will go away and look like the first report image shown above with the fish, but not for long. Like this meme, the message will never go away forever, but appear every time I or someone else opens the report.
Good Luck Getting Rid of the Custom Visualization in Power BI
If you were smart enough to add the custom visualization to the Power BI using the Power BI Desktop, you are in luck. I don’t have that kind of luck. I loaded it to the web application. Why does it matter where you loaded the visualization? Because you can’t get rid of it in the web version. Check out this link from Microsoft and scroll down to this part “Once you import a custom visual you cannot remove it from the report.” Even when I got rid of any use in the report to the custom visualization the link to the custom visualization is still there. The warning message never goes away. If you added the custom visualization to Power BI Desktop, you are in luck as Teo Latchev has posted instructions for you to get rid of the visualization in Power BI Desktop. It’s not a straight-forward process, but at least there it is possible.
So Long and Thanks for All the Fish
Until I have the ability to change my mind with design issues, which I though was sort of a prerogative, I’ll be staying away from custom visualizations. If I can’t turn the warning message off, I probably will never use custom visualizations. Hopefully you will read this before you had to do what I did, deleted the report and started over.
Yours Always
Ginger Grant
Data aficionado et SQL Raconteur
@Ginger – Definitely appreciate the feedback and want to let you know that we’re working to get fixes out for each of these items. The first – to reduce how often you see the warning – is coming very soon. The second, to allow you to remove custom visuals from a report is being planned right now. It’s just a matter of time before these are addressed and you’ll have what you’re asking for.
Lukasz —
I am really glad that Microsoft is working on getting the fixes out on this item. It is very difficult to determine which items are going to be released in the near future and I am happy to know fixes to visualizations are going to be fixed. I am looking forward to the ability to use the functionality, which I do not feel I can release right now.
–Ginger
Hey – Faisal from the Power BI team here. Sorry about excessive warnings; but please be aware that we are working on this. You should see an improvement roll out very shortly (I am hoping this week). When that goes out, you’ll have to accept the warning just once, and you will be good after that. Not perfect, but much better than every single time.
I know this couldn’t come soon enough, but we’re working on it.
Thanks.
Faisal —
I am really glad that the warning is going to limited to one time. Modifying Power BI in this manner will make it acceptable to clients.
Regards,
Ginger