I decided to order the RS210s because I got a new Garmin computer and wanted the seamless integration. The amount of data available from this dual-sensing setup is fantastic and (after only one ride) I have no regrets about the purchase.
I understand that cheaper dual sensing meter systems exist. If they had identical functionality (which is extensive when looking at my Garmin account) I might be tempted to save the money... but I found that getting to the bottom of that question to be not worth the research.