Something tells me you're feeling leary about this for more than the reason you're stating (sandbox); only meaning, I get the impression you don't have a good warm-fuzzy about this...?
Actually, I don't think I'd go for it. It
seems okay, but why risk your good
PR and great traffic for a max of 2400 per year? Of course you can do this multiple times, but what good does it do your site? If they have a client who later turns bad, gets banned, or whatever - are they going to replace your
PR, get you out of hot water with Google, replace your traffic?
Something tells me this will not go over well in the long run with Google and other engines, but I'm used to being wrong, so who knows?
They're brokering link deals for the sole purpose of raising a lesser sites'
PR boosts ... just doesn't feel right. I realize they guarantee anonimity for both to/from client's, but still doesn't feel right.
Either way, go with your gut. Let me know if you go for it, I'd be interested to see if this pans out in the long run. (PM, I wouldn't advertise it...)
Good luck either way!
w®m