I use them for trolling stripers or tuna but never for flounder.
What I found that catches fluke when they have lock jaw to most other lures or bait is a viper spoon.
Where I mainly fish flounder is on a reef 10 miles off the shore and we get caught on the wrecks and structure plus there are a lot of fish traps out there. Using an umbrella rig would guarantee snags and lost terminal tackle.
My ability to remember lyrics from songs of the 60's far exceed my ability to remember why I walked into the kitchen