I have a Sigma Onyx Fit heart rate monitor. The Onyx series are digital while the PC series are analog. The PC-15 has a good reputation and the price is good. My advise would be that I suspect that these are old stock that have been sitting around for a while so its likely that they will need new batteries. Not necessarily a deal breaker but something to consider.
I bought my Onyx Fit model on eBay at a good price and I needed to replace the batteries straight up too.