From what I know, their main cause is overall just and they have done good work infiltrating places with hidden cameras and recording/exposing animal cruelty...
...But their publicity stunts, probably the big thing they're known for these days, are almost always stupid and imo do more harm than good by turning potentially sympathetic people against them, and possibly by extension animal rights.
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Most people I know in the ALF, started as teenagers in PETA. I think PETA serves a useful purpose in introducing people to the cause and their methodology (the celebrity "naked" anti fur posters, the colorful graphic design and merchandise, the use of obvious trolling to draw attention to their cause) appeals to teenagers who are new to these things.
Plus PETA pushing for vegan and vegetarian options in restaurants has made things much easier for those of us who don't eat meat in my lifetime. Back when I was a kid, my mum couldn't get me a happy meal because they only had meat options. Now they have multiple veggie and vegan options. That's a good thing that's almost exclusively down to them.