I'm not sure What the Diamondback Poseidon Triton is (But I don't believe Poseidon Triton is an official DB model), but I would look at the Diamondback Century bikes. If you can score a DB corp discount code (which I'm sure some folks on here will share?) you can get the Century for $409 and the Century 2 for $1169 and the 2 has an ultegra setup. That's a heck of a deal. (2017 models are on clearance right now).
If it were me, I'd go DB and I'd act fast
They're comfortable bikes and they're fast