Answer: Keeping the Miragedrive chains and idler cable tension right will mean optimal performance and reduced risk of mechanical issues
If they become loose there is a possibility of causing damage to the sprocket, especially if pedaling harder and faster. Adjust fin tension by turning the 1/4" nylock nuts that secure the chains and idler cable to the drum.
Each chain and cable should be somewhat taught, but not over-tightened. Anything from 1mm to 3mm in sideways play is probably acceptable - any less and they are too tight, any more and they are probably too loose. You'll know if they are too tight by actuating the pedals with your arms. If you can feel resistance back them off a little and try again.
Out of the packet the front chain is typically tightened marginally than the rear, but it won't hurt to have them both at exactly the same tension. Check chain tension regularly. If a particular chain or cable tends to become loose on a recurring basis, the 1/4" nylock nuts securing them might need to be replaced.
If in doubt pop in to your local Hobie kayak dealer and get them to inspect your Miragedrive and demonstrate how tight the chains should be