I think the idea is to use the reed relay to trigger the TRIAC, not drive the load directly.
Lots of reed relays aren't isolated enough to protect against electric shock, but that's a non-issue here, assuming the 24V or trigger circuit aren't floating at hazardous voltages i.e. are both isolated from the mains.
I think an opto-coupler and TRIAC is a good idea. The only alternative, other than a relay, is a MOSFET solid state relay, consisting of two back-to-back MOSFETs and a photovoltaic opto-coupler, such as the VOM1271, but it's more expensive.