Are Speedo 13.5cm briefs actually Sungas
 

https://www.allensswimwear.co.uk/spe...-8-00518818766

Swim briefs should be brief or they are something else and 13.5cm isn't brief. 3cm or 5cm even 7cm is brief.
Square cut swim suits are about 13.5cm at the side but they have an inside leg if only short maybe 2cm. These are somethng else.
The only something else that I can think of that is 13.5cm at the side and has no inside leg is the Bazillian style Sungas.
So in conclusion have Speedo's 13.5cm swim briefs become Sungas and should I buy some as they are on offer?

I think a brief should have a clear triangle shape from the front and rear.
I've found that 8 cm sides are about the maximum for this.
Anything bigger than that is a trunk or square cut as far as I am concerned .
However if you want something like that just go for it.