...Has anyone used any sort of spring
kickstarter/sludge eater and felt it was worth it?

I have been using Bacta Pur for 7 yrs now and have not cleaned my pond
bottom since, with no accumulation of sludge or dead plant material, except
in the spring as I don't use it after I quit feeding the fish in the fall,
so it does build up over the winter until I start using it again in the
spring/summer - before that I was scooping out as much as possible with a
fine net 3 or 4 times a yr whenever I could (around the plants and baskets)
Gale :~)
PS - and yes I do sell the stuff locally , but am not interested in spamming
this NG in any way - the info above is for information only