I know there's been previous discussion on this in the past one for example here:
https://vborg.vbsupport.ru/showthread.php?t=140746
What I can say (imo) is this, if your not familiar with SEO, purchase vBSEO as it works out of the box so you install and let it fly. Just like anything else in life if you want more you must spend time configuring it how you wish it to be. You can "SEO" your forum without it however again if your not experienced with SEO or don't have the time to check into it and implement properly then their price is not too harsh

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As always imo and remember there are other past threads on here and other sites with this same question and all sorts of answers from experienced site owners as well so don't be afraid to search, that way your well informed before you make a decision

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