There should be lots of reviews around for both services. Just look for "Adult Friend Finder" and "Heypersonals".
I also paid for heypersonals for a month or two before coming to Taiwan, getting to know some people (both sexes) with similar taste in music, so that I knew someone before I arrived here. From my experience for this kind of thing heypersonals works well, but or course you also have some girls there that will want to hook up with you even you are really just looking for friends (as in "pen pals" or "sports / activities partners"). I didn't run into many fakes, obvious hookers or whatever there, at least not as far as I could tell. That was 3 years ago, though. Mabye one or two times i recognized pictures of celebrities as profile pics, I guess those were jokes or fakes. Also I saw a few profiles being closed/deleted by the website management, with pretty suggestive names... I guess those would have been something fishy as well. All in all, far as I can tell lots of Taiwanese people which are interested in travelling abroad, learning languages, or simply making foreign friends are on that site. I think if you are open and genuine, you can make friends there. It simply increases the chances of getting to know someone with similar interests.
Two of my friends (girls) also used Heypersonals for finding friends (nothing else - as far as I know ^^), and for them it worked. Well, I think girls don't pay on such kind of sites, so no risk for them anyway.
I also know at least one American English teacher and one Taiwanese girl that were using the Adult Friend Finder for their sexual adventures, and while they didn't go into details when we talked about that, it seems it worked out for them. At least I think that means not all profiles there are fakes.
All in all there seem to be genuine people online in that kind of sites - but on the other hand, free stuff like facebook, myspace, and all kinds of blogs (plus MSN/Live Messenger) can be used to find friends online as well. For the adult stuff, the language exchange parts of tealit etc. seem to have a pretty bad (good?) rep, but I have no experience with that. I guess it all depends on what you are looking for.
Keep in mind that in Taiwan it seems pretty normal to find friends over the Internet, also a kind of a nerdy dating culture here I feel. So even though in your home country this kind of website might be considered seedy, desperate or whatever, chances are that Taiwanese think different.