I use it for buying(/trading) for the cards I’m still missing in my collections. Here my current post: https://www.reddit.com/r/pkmntcgtrades/comments/ef5mz5/nl_ww_w_pikachu_seviper_and_some_other_tcg_cards/
I think I’ve been using it for three years now, updating it every 2-3 months. Thus far I’ve only been able to find one new Pikachu through it, which I traded for a duplicate of mine. I’ve also sold duplicated Pikachu cards twice (despite only having a WTB post… 
). And did a second trade a few months back (not for a Pikachu, though).
Overall in terms of buying with the specific cards I’m looking for, posts like the ones I’ve got aren’t very useful on any media. Even here on the Efour forum I’ve only been able to buy one Pikachu in all the time I had my WTB post (although I did purchase a few more cards from E4 members, it was mostly through Instagram or tips they gave me of current eBay auctions). I mostly buy the Pikachu cards I’m still missing by keeping a close eye on eBay, CardMarket, Yahoo Japan, and some Facebook groups regarding errors. Two years ago I used to check eBay and CardMarket (where possible) every day, but these days I only check once a week on average.
Greetz,
Quuador