my magnets were not very effective... they got off the top layer but didnt really scrape off the serious stuff.. but maybe its just cause i had some algae problems..
anywho i think the best way to get algae off is plain 'ole scrubbin! but there's the downside of gettting wet.. especially with tall tanks that require you o go in as far as the armpits.. not fun. so get some but i would definitely get the strongest ones you can possibly get!