In my opinion, services like this tend to target new expats that are unsure of how they are going to get their "precious American goods". I agree that it really doesn't make much sense for smallish items unless the vendor absolutely will not ship overseas. There are some companies that will not ship to some Eastern European countries, African countries, etc due to the high amounts of credit card fraud.
The personal shopping, though, is helpful because there are many American sites that will not accept a non-US based credit card. I can't tell you how many packages I have accepted and then shipped myself to my SIL from Target and Gap. Which is aggravating because they do have the Gap in the UK but just not what she wants, but I digree.
I see Bongo ads on the expat sites frequently but I have never encountered anyone who has used them specifically. I think that if you've been shipping overseas for eight years you're fine without them. Unless you wanted to just go with them to maybe drum up so extra business. I'm not sure that I would want to install their stuff on my site though. I think you're right to be cautious there.