Yes DF. I've used it during Spring and Summer for the past couple of years. Used it only yesterday in fact, for the first time this year.
I'm not sure if it helps to keep the water clear or not - right now it is beginning to get murky, so will see how it looks in a few days time.
I have some brilliant stuff to keep the slimy blanket weed away. My local aquatics store asked me to try it for them last summer. Gave me a kilo of it and I only need 220g each time I use it. Last year I seem to remember that using it just twice kept the water clear of the slimy weed and it works within a day or two. Fantastic! It's called Kusuri Ecogold Blanket Weed Eradicator. They have a website :-
http://www.kusuri.co.uk/shopping.php?class_id=124 and email is :-
mailto:sales@kusuri.co.uk.