They WILL remove excess phosphate, unfortunately in all likelyhood the plants will definitely suffer, and the algae will probably accelerate, and bloom.
I fell for this marketing Hog Wash back in the day. I tried damn near all of them, and never achieved this low phosphate / algae free nirvana. So I scrapped the program, and started on a strict EI regimen W/ liberal Co2. Guess what ? That Bad Ole Algae just went away. Go Figure ? I used the remnants of the program for phosphate deprivation experiments with plants. Can you say Crooked Babies ? No phosphate = UGLY crooked @$$ Plants !
If it were a controlled SW reef environment, and phosphate were an issue I'd say sure WTH ? An Aquatic Herp Tank...Maybe ? FW Planted Aquariums... No Way !!!
Rowaphos is in my opinion the best (Most Efficient), but as far as I'm concerned it may as well be poison. I had some backwash out of a reactor into the sump once. Naturally being a good custodian I did a waterchange. Unfortunately that drain goes to grey water for my lawn. To make a long story short I had a reverse mohawk in the very center of my yard for 2 years, and it's only now coming back, and that only after applying several applications of phosphate, and the past 2 years irrigation. We don't often think of filter media as a contaminant but absolutely DO NOT dump this rubbish down the drain or dump it in the yard.
I DO loath Boogie Man stories on forums. It's your call, and your decision. Personally I'd re-invest the money in Co2 or TMG and call it a day !
Be Very Careful What You Wish For.
Excess algae is the result of a Nutrient "Imbalance". Stick with W/C's and EI dosing. Mi Dos Centavos or .021152 Canadian, Prof M.