I believe Bill Cody indicated some weeks back that in northern venues Water Primrose is mostly accepted as a decent aquatic plant. But in the areas of the country where a hard freeze doesn't happen or at least not often it can be very invasive.
Mine will go years sometimes without blooming/coming on, no idea why. This is the first year since 2011 that I've had what I'd call 'mostly full' coverage, which means to me that 70-80% of the bankline has it.