tell me about light movers

So recently I've been trying to find info about light movers and their effectiveness to increase my plant numbers without going crazy on electricity. But I cant seem to find any good info from people who have used them. So any info, past experiences, tips you could give me would be greatly appreciated.
First off will my weight per plant go down drastically?
How many more plants could I get under a 4' light mover?
Are they really worth it or would I just be better off with another light?
 
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