In one thread or another a representative for Optima got involved in this discussion. He confirmed that there is no basic difference in the blue top and yellow top size 34 battery. The blue top which is intended for marine service has some extra wing nut lugs on each terminal, but that is it. There is a difference in the guarantee, and I recall the yellow top guarantee is better. Not sure on price.I looked up the Optima blue top batteries, they seem pretty reasonable at around $175 at Amazon. As much as I would like to save some money with a regular battery, the risks seem a bit too high.
But neither size 34 has a vent connection. The Prius model does, and while a little smaller and lower in capacity it should work fine. It would be the safest choice. This battery doesn't start the motor. The only need for capacity and it would be best represented as Reserve Capacity is to power up the security and smart key system when the vehicle is turned off. A bigger battery could be left longer without it going flat. But we are probably talking months, not days.
I'm hoping by the time mine fails in 2020 or so, Optima or someone else will be making a size 34 AGM battery with a vent connection.