Leadtek adapters were used by Packet8 here in the USA for many years. They may have worked with that service but I can tell you from my experience that they were horrible to connect to an Asterisk server. Not only would they simply refuse to connect at various times, but they kept generating an invalid SIP packet containing the message "Content To Short" (with "too" misspelled) that would appear repeatedly on the CLI and in Asterisk's log file. Every single user I knew of that had them gave up and bought something else (most bought OBi110's or OBi100's, and in all cases the OBi's worked beautifully) because the Leadtek's were so unreliable when connected to Asterisk. Of course all this is just my opinion, but there is no way I'd ever willingly let another Leadtek device onto our server. Someone else's experience might be different, but that's my opinion.
Sometimes VoIP adapters have many settings for a reason... such as by tweaking the right setting, you might actually be able to get the thing to work the way you want it to!